9.2.1.2 Chemical Reactions
Describe the role of valence electrons in the formation of chemical bonds.
Explain how the rearrangement of atoms in a chemical reaction illustrates the law of conservation of mass.
Describe a chemical reaction using words and symbolic equations.
For example: The reaction of hydrogen gas with oxygen gas can be written: 2H2 + O2 → 2H2O.
Relate exothermic and endothermic chemical reactions to temperature and energy changes.
Overview
MN Standard in lay terms:
Chemical reactions occur when the atoms of a substance interact with atoms of another substance. This involves changes of energy and the transfer or sharing of the atoms' electrons. These chemical changes can be described symbolically with a chemical formula.
Big Idea:
Because so much of the natural world revolves around chemical reactions (photosynthesis, Kreb's cycle, human systems, etc.) it is important that students understand the experimental nature of science and how explanations and understandings that are currently taught in a classroom come from the investigation of several processes, ideas and people and that they can change as more information is discovered.
Many chemical methods are currently used to solve problems such as de-icing planes, burning fossil fuels for energy and transportation as well as preserving food. However, because of new knowledge and new substances, there may be better and safer ways of using what we already have. Engineering is a methodical way to study these processes and recommend new solutions for everyday problems and possibly help keep the environment cleaner.
The re-arrangement of atoms during chemical reactions involves the breaking and making of chemical bonds involving energy. The atoms themselves do not change in mass because only the outermost electrons of the atom are involved in the chemical change.
MN Standard Benchmarks
9.1.1.2.2 Evaluate the explanations proposed by others by examining and comparing evidence, identifying faulty reasoning, pointing out statements that go beyond the scientifically acceptable evidence, and suggesting alternative scientific explanations.
9.1.1.2.3 Identify the critical assumptions and logic used in a line of reasoning to judge the validity of a claim.
9.1.2.2.1 Identify a problem and the associated constraints on possible design solutions.
For example: Constraints can include time, money, scientific knowledge and available technology.
9.1.2.2.2 Develop possible solutions to an engineering problem and evaluate them using conceptual, physical and mathematical models to determine the extent to which the solutions meet the design specifications. For example: Develop a prototype to test the quality, efficiency and productivity of a product
9.2.1.2.1 Describe the role of valence electrons in the formation of chemical bonds.
9.2.1.2.2 Explain how the rearrangement of atoms in a chemical reaction illustrates the law of conservation of mass.
9.2.1.2.3 Describe a chemical reaction using words and symbolic equations. For example: The reaction of hydrogen gas with oxygen gas can be written: 2H2 + O2 → 2H2O.
9.2.1.2.4 Relate exothermic and endothermic chemical reactions to temperature and energy changes.
The Essentials
NSES Standards: NSES Chemical Reactions Standards
Chemical reactions occur all around us, for example in health care, cooking, cosmetics, and automobiles. Complex chemical reactions involving carbon-based molecules take place constantly in every cell in our bodies.
Chemical reactions may release or consume energy. Some reactions such as the burning of fossil fuels release large amounts of energy by losing heat and by emitting light. Light can initiate many chemical reactions such as photosynthesis and the evolution of urban smog.
A large number of important reactions involve the transfer of either electrons (oxidation/reduction reactions) or hydrogen ions (acid/base reactions) between reacting ions, molecules, or atoms. In other reactions, chemical bonds are broken by heat or light to form very reactive radicals with electrons ready to form new bonds. Radical reactions control many processes such as the presence of ozone and greenhouse gases in the atmosphere, burning and processing of fossil fuels, the formation of polymers, and explosions.
- AAAS Atlas of Scientific Literacy
An atom's electron configuration, particularity the outermost electrons, determines how the atom can interact with other atoms. Atoms form bonds to other atoms by transferring or sharing electrons. 4D/H1bc
An enormous variety of biological, chemical, and physical phenomena can be explained by changes in the arrangement and motion of atoms and molecules. 4D/H7b
Chemical energy is associated with the configuration of atoms in molecules that make up a substance. Some changes of configuration require a net input of energy whereas others cause a net release. 4E/H4
An atom's electron configuration, particularity the outermost electrons, determines how the atom can interact with other atoms. Atoms form bonds to other atoms by transferring or sharing electrons. 4D/H1bc
When substances interact to form new substances, the elements composing them combine in new ways. In such re-combinations, the properties of the new combinations may be very different from those of the old. SFAA p. 47
Energy appears in different forms ... Arrangements of atoms have chemical energy. 4E/M4ac
Benchmarks of Science Literacy Project 2061 Benchmarks of Scientific Literacy Online
Atoms often join with one another in various combinations in distinct molecules or in repeating three-dimensional crystal patterns. 4D/H7a
An enormous variety of biological, chemical, and physical phenomena can be explained by changes in the arrangement and motion of atoms and molecules. 4D/H7b
Chemical energy is associated with the configuration of atoms in molecules that make up a substance. Some changes of configuration require a net input of energy whereas others cause a net release. 4E/H4*
An important kind of reaction between substances involves the combination of oxygen with something else-as in burning or rusting. 4D/M6b*
No matter how substances within a closed system interact with one another, or how they combine or break apart, the total mass of the system remains the same. 4D/M7a*
The idea of atoms explains the conservation of matter: If the number of atoms stays the same no matter how the same atoms are rearranged, then their total mass stays the same. 4D/M7b
Common Core Standards
2010 Literacy Standards - Reading Benchmarks: Literacy in Science and Technical Subjects 6-12
Integration of Knowledge and Ideas Benchmark 11.13.7.7 Integrate and evaluate multiple sources of information presented in diverse formats and media (e.g., quantitative data, video, multimedia) in order to address a question or solve a problem.
Common Core Language Arts Standards: Students can write a laboratory report in the proper form and using their knowledge of technical writing skills. Common Core Standards addressed:
RST.9-10-1. Cite specific textual evidence to support analysis of science and technical texts, attending to the precise details of explanations or directions.
RST.9-10-2. Determine the central ideas or conclusions of a text; trace the text's explanation or description of a complex process, phenomena or concept; provide an accurate summary of the text.
RST.9-10.3. Follow precisely a complex multistep procedure when carrying out experiments; taking measurements or performing technical tasks, attending to special cases or exceptions defined in the texts.
Misconceptions
"The usual high-school science "experiment" is unlike the real thing: The question to be investigated is decided by the teacher, not the investigators; what apparatus to use, what data to collect, and how to organize the data are also decided by the teacher (or the lab manual); time is not made available for repetitions or, when things are not working out, for revising the experiment; the results are not presented to other investigators for criticism; and, the correct answer is known ahead of time." (Benchmarks of Scientific Literacy - Scientific Inquiry)
Middle- and high-school student thinking about chemical change tends to be dominated by the obvious features of the change. For example, some students think that when something is burned in a closed container, it will weigh more because they see the smoke that was produced. Further, many students do not view chemical changes as interactions. They do not understand that substances can be formed by the recombination of atoms in the original substances. Rather, they see chemical change as the result of a separate change in the original substance, or changes, each one separate, in several original substances. Atlas of Science Literacy
The word "substance" is often used by students to refer to any form of matter. Make sure they understand a "substance" is only an element or compound. (Handlon, 2011)
Because the physical properties of reactants change during a chemical reaction that produces a new chemical substance, students often think that the reaction has created a new substance made of totally different kinds of atoms and elements than the ones originally mixed rather than understanding that the new substance is a re-arrangement of the original atoms and no new atoms were made. (Handlon, 2011)
Vignette
Mr. Dalton walks into his ninth grade Physical Science class and tells students they will be doing a lab activity today and should take out their journals. He has students go to their lab station in their groups where they would find a balance and a bag of five metal bolts and ten nuts. Students were to mass all of the items together and record the total mass. They were to then link the nuts and bolts together in various combinations (such as two nuts to each bolt, two bolts with 5 nuts and the others with none etc.). Students were to describe each combination and then record the total mass. They were to complete three or four different combinations. (Benchmark: 9.2.1.2.2 Explain how the rearrangement of atoms in a chemical reaction illustrates the law of conservation of mass.)
For the follow up students were asked to write (or draw) the change in combinations by starting with the original nuts and bolts then writing an "arrow" (which he told them would symbolize 'changes to') and then writing the final combination. For example five bolts + ten nuts → five bolts with two nuts each. Then students were told to imagine that they have 8 atoms "A" and 12 atoms "B" then write similar "equations". For example 8 A + 12 B → 8 AB + 4 B or 8 A + 12 B → 4 A2B + 8 B. (Benchmark: 9.2.1.2.3 Describe a chemical reaction using words and symbolic equations.)
After students had completed this activity they were to sit down and discuss the following questions with their lab partner and come to a consensus answer.
1. How does the number of nuts and bolts you always have after rearranging them compare to the number of nuts and bolts that were there before rearranging?
2. How does the of "atoms" of A and B after rearranging them compare to the numbers of atoms of A and B to before rearranging them?
3. Use the ideas of Dalton's Atomic Theory studied in the previous unit to explain any differences. Be specific in citing one of Dalton's points in answer.
The next class period Mr. Dalton had the students do another lab activity. (Benchmark: 9.2.1.2.2 Explain how the rearrangement of atoms in a chemical reaction illustrates the law of conservation of mass.) At each lab station was a centigram electronic balance and two small beakers each containing a solution. One beaker contains about 10 ml of a 0.1 M solution of Silver Nitrate (AgNO3), the other contains a similar volume of 0.1 M Sodium Chromate (Na2CrO4). Students are given a handout with some guidelines. They were first asked to record as many observations about the two solutions as they can.
Next they were to place both beakers on the pan of the electronic balance. They were to measure and record the total mass of the system. With goggles on they were to pour one solution into the other then place both beakers back on the balance. They were to record the total mass of the system again as well as all the observations they can. They finish by rinsing out the glassware and returning to their seats.
Next students are put into groups of three to compare notes and discuss their observations. Mr. Dalton gives each group a set of questions which they are to discuss and then record a group consensus answer in their journal. These questions include the following:
1. From your observations describe three changes in the properties of the materials before mixing from those after mixing.
2. Do you think the product after mixing was chemically the same (had the same kinds of atoms) after mixing as before mixing. Explain your answer. What evidence from your observations supports your answer?
3. How did the mass change comparing the mass before and after mixing?
4. If your answer to question number two was that the product was not chemically the same, why didn't the mass change? If your answer to question number two was that the product after mixing was chemically the same why did it appear to have different physical properties?
After students have had time to discuss the questions in their groups and have written their answers Mr. Dalton asks students to share their answers and he records some responses on the board. Most groups are in agreement about their common observations from the activity and their answers to question number one. However, groups differ on their answer to number two with some of the groups concluding the product was chemically the same but others concluding it wasn't. Mr. Dalton does not respond, he only records the number of groups for each answer and then moves on to the next question. All groups are in agreement that there was no change in mass.
Now Mr. Dalton asks the groups who concluded the product was not chemically the same to explain why the mass didn't change. A variety of answers are given. He tells the groups who concluded the product was chemically the same to take note and think of questions to challenge the other groups answers. He then reverses the positions and has the groups who thought the product was chemically the same to respond and the others to note questions.
Mr. Dalton then asks, "Who's idea is supported with the best evidence?" He allows students to question their peers who had different conclusions and the others to reply. The discussion is kept going until near the end of the period. "Your homework," he tells the class, "is to think of what we might be done scientifically to determine which response is supported." Students are to write down their answers in their journals with the rest of the activity for a "journal check" the next day. (Benchmark: 9.1.1.2.3 Identify the critical assumptions and logic used in a line of reasoning to judge the validity of a claim and Benchmark: 9.1.1.2.2 Evaluate the explanations proposed by others by examining and comparing evidence, identifying faulty reasoning, pointing out statements that go beyond the scientifically acceptable evidence, and suggesting alternative scientific explanations.)
This and the previous activity were used to "springboard" into the second chemistry unit on chemical reactions, law of conservation of mass and balancing chemical reactions. Mr. Dalton spent the next class period introducing some vocabulary such as reactants, products, chemical change, chemical reactions and "balancing chemical equations" using examples from the nuts and bolts then moving to the "hypothetical" atoms A & B then to actual examples of chemical reactions. The reactions used were simple and did not use any that involved polyatomic ions.
Mr. Dalton moved through the unit progressing from the concrete to the abstract. Students did an activity called "It's in the Bag" that allowed them to examine the energy changes which accompany reactions (introducing the terms "exothermic" and "endothermic"). The activity also helped students understand how the law of conservation of matter can seem to be "violated" unless the total mass of all reactants and products is considered especially when some of these may be gases. For example students could mass baking soda and vinegar together and then mix them and mass them after. How would they account for the "loss" of mass?
Mr. Dalton provided his students with opportunities to experience a variety of chemical reactions in the laboratory. In each example students were asked to make their observations then write the balanced question for the reactions. (Benchmarks: 9.1.1.2.2 Evaluate the explanations proposed by others by examining and comparing evidence, identifying faulty reasoning, pointing out statements that go beyond the scientifically acceptable evidence, and suggesting alternative scientific explanations. and 9.2.1.2.3 Describe a chemical reaction using words and symbolic equations.)
When the students have had experience balancing reactions Mr. Dalton asks students to write the electron configuration of nitrogen, potassium and oxygen. He then asks the students to determine the number of outermost (valence) electrons. Mr. Dalton reviews with the students the manner in which atoms can bond by transferring or sharing valence electrons. (Benchmark: 9.2.1.2.1 Describe the role of valence electrons in the formation of chemical bonds.)
Resources
Instructional suggestions/options
Students should not be allowed to conclude that the mutability of science permits any belief about the world to be considered as good as any other belief. Theories compete for acceptance, but the only serious competitors are those theories that are backed by valid evidence and logical arguments. (Benchmarks of Scientific Literacy - Scientific Inquiry)
The nature of science and engineering need to be clearly differentiated in the classroom.
Teachers can collaborate closely with colleagues in grades 6-8 to ensure a progression of learning in the sub-strand matter. A close alignment of 6-8 curriculum will best prepare students for more advanced work in chemistry.
To further engage students, teacher's could begin this series of lessons with the chemistry in a bag activity, followed by nut n' bolts and finish with a demonstration of chemical reactions.
As the teacher prepares to teach this standard pay close attention to the national documents (NSES and Benchmarks) for deeper understanding of the intent of the standard.
When first teaching students how to "balance" chemical reactions Mr. Dalton showed them a "trick" for helping them keep track of the kinds and numbers of atoms on each side of the equation. He encouraged students to write a "box" around each formula in the equation. Students were told that a number (called a "coefficient") could be put in front of each of each box but that no numbers could be changed inside the boxes. Any number put in front of a box would then multiply everything inside the box. This helped students avoid balancing equations by changing the formulas of the reactants and products.
"Before graduating from high school, students working individually or in teams should design and carry out at least one major investigation. They should frame the question, design the approach, estimate the time and costs involved, calibrate the instruments, conduct trial runs, write a report, and finally, respond to criticism." (Benchmarks of Scientific Literacy - Scientific Inquiry)
Suggested Labs and Activities
For a complete description of chemistry in a baggie Lawrence Hall of Science GEMS "Chemical Reactions" Guide GEMS "Chemical Reactions" Guide
The Big Chill Students investigate the endothermic reaction involving citric acid, sodium bicarbonate, and water to produce carbon dioxide, water, and sodium citrate
Students should have a variety of experiences observing chemical reactions in the lab. They can be given the basic "skeletal equation" and asked to balance it. Examples of reactions would include zinc metal into Hydrochloric acid to make hydrogen gas (test with a glowing splint), reactions of solutions that make precipitates such as copper (II) chloride with sodium carbonate, combustion of metals such as magnesium or iron (steel wool) and single displacement reactions such as magnesium metal with silver nitrate. (Benchmark: 9.2.1.2.3 Describe a chemical reaction using words and symbolic equations.)
One "engineering" application for this topic would be to have students measure the "heat of solution" (heat generated when a salt dissolves in water) of some compounds such as sodium chloride, calcium chloride, sodium hydroxide. Students then do research to find a low cost salt that might be sold as a "de-icer" for homeowners. Students determine which salt will produce the most heat safely and without environmental hazards at the lowest cost to produce. (Benchmarks: 9.1.2.2. Engineering design is an analytical and creative process of devising a solution to meet a need or solve a specific problem. 9.1.2.2.2 Develop possible solutions to an engineering problem and evaluate them using conceptual, physical and mathematical models to determine the extent to which the solutions meet the design specifications.)
Additional resources
TeachEnginneering.org - The TeachEngineering Digital Library exists to provide teachers with the curricular materials to bring engineering into the K-12 classroom for a single day, a unit, or even an entire course.
eGFI - Here you will find a variety of tools to boost your students' math and science skills, enliven the classroom with engineering projects, expand your own professional horizons and stay informed.
PA Governor's Institute For Physical Science Project- Conservation of Matter (Benchmark: 9.2.1.2.2 Explain how the rearrangement of atoms in a chemical reaction illustrates the law of conservation of mass.)
Mission Impossible: Law of Conservation of Matter Lab Activity (Benchmark: 9.2.1.2.2 Explain how the rearrangement of atoms in a chemical reaction illustrates the law of conservation of mass.)
Dealing with student misconceptions about the Law of Conservation of Mass The Science Teacher Archives: Overcoming Misconceptions
Vocabulary/Glossary
- Exothermic: Chemical reaction or process which releases heat energy.
- Endothermic: Chemical reaction or process which absorbs heat energy.
- Conservation of mass: Mass is neither created nor lost in an ordinary chemical reaction.
- Balanced chemical equation: The symbols and numbers of atoms which are equal to the numbers and kinds of atoms from the start to the completion of a chemical reaction.
- Reactants: The kinds and numbers of atoms at the beginning of a chemical reaction.
- Products: The kinds and numbers of atoms which result from a chemical reaction.
- Valence electrons: The outermost electrons of an atom which are involved in the atom's formation of bonds and chemical reactions.
- Law of Conservation of Mass": Atoms are neither created nor destroyed during chemical reactions, they are only rearranged into different combinations.
- Coefficient: The number before a compound or element in a chemical reaction giving the number of units of that substance.
- Subscript: The number below and to the right of an atom or group of atoms in a chemical reaction that gives the number of units of that atom or group.
Balance a chemical equation.
Recognize that the number of atoms of each element is conserved in a chemical reaction.
Describe the difference between coefficients and subscripts in a chemical equation.
Translate from symbolic to molecular representations of matter.
Reactants, Products and Leftovers
Vernier temperature probes can be used to determine whether reactions are exothermic or endothermic Vernier sensors (Benchmark: 9.2.1.2.4 Relate exothermic and endothermic chemical reactions to temperature and energy changes.)
Engineering Education Lab Books from Vernier
Website with "game" for balancing equations of chemical reactions Classic Chembalancer (Benchmark: 9.2.1.2.3 Describe a chemical reaction using words and symbolic equations.)
There are applications of math skills used in balancing chemical reactions. (Determine the meaning of symbols, equations, graphical representations, tabular representations, key terms and other domain-specific words and phrases as they are used in a specific scientific or technical context relevant to grades 9-12 texts and topics. 9.13.4.4 & 11.13.4.4)
Family and Consumer Science connections with the "chemistry" of cooking and food preparation.
Automobile mechanics connections with the chemistry of internal combustion engines.
Art connections with the chemistry of paint and ceramic glazing.
Life Science connections with the chemical reactions such as photosynthesis and respiration.
Physics connections with energy transfers and Law of Conservation of Energy.
Assessment
Assessment of Students
Have students a create a multi-media presentation using google docs 'power point' to illustrate their understanding of the standard(s). Level: Synthesis
A student places a candle on a piece of cardboard on an electronic balance and measures the mass. After the candle is ignited and has burned for a while the student again measures its mass. The mass of the candle is now less. From this observation the student concludes that burning a candle does NOT follow the Law of Conservation of Mass.
Has the student made a correct conclusion? If not, what would you tell the student to 'correct' the student? Is the burning of a candle an "exothermic" or "endothermic" reaction? Level: Analysis
How are an atom's electrons involved in a chemical reaction? Explain which electrons are involved and what changes they undergo in a chemical reaction. Level: Application
Assessment of Teachers
How might a teacher respond to a student's query "Why do I need to know this?"
What are common examples of chemical reactions (cooking, campfire, etc) which will assist in student understanding of these concepts?
What are some examples of endothermic and exothermic chemical reactions or processes from everyday experience that students could relate to or that you might demonstrate to help students understand these terms?
Differentiation
Struggling and At-Risk
Engage struggling students with activities which are fun and involve food. Give students toothpicks, gumdrops and marshmallows. Students then "build" the reactants and products in a chemical reaction to illustrate the changes and law of conservation of matter. When finished the students can "consume" the ingredients in another chemical reaction.
From Teaching Science to ELLs NSAT journal The Science Teacher March 2011
1. Provide opportunities for input and output
There are many strategies a teacher can implement to make input comprehensible-such as using cognates, visuals, simulations, and models; rephrasing; or allowing the learner to explore first. Accommodations such as this benefit not only ELLs, but also students with diverse learning preferences. Teaching Strategies for ELLs by Nazan Bautista and Marcha Castaneda The Science Teacher March 2011
The strategies outlined in the vignette which involve "hands on" concrete activities with little or no vocabulary are excellent for engaging ELL students. The ELL student is able to develop the concepts then attach vocabulary to those.
2. Provide opportunities for interaction
Another factor for ELLs' success in language acquisition is interaction, an activity that connects input and output.Interaction serves as the foundation for language development because it requires ELLs to comprehend language iinput, produce language output, and negotiate meaning with others. Through interaction, ELLs not only develop their scientific communication skills, but also clarify their understanding with classmates who are more proficient in English. For this reason, carefully planned small-group activities, can be an effective instructional strategy for ELLs. Teaching Strategies for ELLs by Nazan Bautista and Marcha Castaneda The Science Teacher March 2011
For those students who are Gifted and Talented have them research methods for recycling valuable resources such as copper from wire or gold from electronic devices. How is recycling an application of the Law of Conservation of Matter?
Students can research the Chinese discovery of gunpowder and how the exothermic combustion of gunpowder is used.
Students with ADHD are often "kinesthetic learners". These students are more focused when using materials to represent their thinking. When first balancing simple equations have them use a molecular model kit to build the reactants then take them apart to form the products.
Parents/Admin
Administrators
An administrator observing a classroom working on this unit should see students engaged in observing examples of chemical reactions and practicing science safety while doing so. Students might be examining reactions in laboratory activities or observing teacher demonstrations.
You can reinforce the concepts of chemical reactions by pointing out examples at home. These might include reactions involving heating and cooling your home, cooking, bleaching clothes, rusting of outside furniture and others.