Alaska Science Performance Standard L4/A8a

	Alaska Science Key Element A8a A student who meets the content standard should understand the scientific principles and models that describe the nature of physical, chemical, and nuclear reactions (Energy Transformations).

Performance Standard Level 4, Ages 15–18

Students explain how the absorption or emission of energy is related to physical, chemical, and nuclear reactions and explains how these reactions can be quantitatively accounted for in terms of changes in arrangements of neutrons, protons, electrons, atoms or molecules.

Sample Assessment Ideas

Students perform flame tests on Li, Na, Ba, and Cu salts; explain the observations in terms of photon emissions and energetics.
Students write balanced equations to account for the rearrangement of atoms in chemical reactions. (NOTE: teacher provides lists of reactants and products.)
Students write balanced equations to account for the rearrangement of neutrons, protons, and electrons in nuclear reactions such as radioactive decay, uranium fission, and hydrogen or helium fusion. (NOTE: teacher provides lists of reactants and products.)

Expanded Sample Assessment Idea

Expanded Sample Assessment Idea

Students perform a standard calorimetry experiment to show that the energy release when an acid is mixed with a base depends on the exact amounts of acid and base reacted.

Materials solutions of 1M HCl and 1M NaOH styrofoam cup, a covering for the top (“take-out” coffee cups with lids) thermometer stirrer (plastic) graduated cylinders or burettes Procedure NOTE: Proper safety procedures must be followed! Students will: Measure amounts of acid and base solutions (different students in class use different amounts). Measure temperature of both solutions—equilibrate at room temperature) Rapidly pour both solutions into cup; attach cup covering; insert thermometer into opening in cup covering; measure temperature as a function of time; record and plot data. Compare results with other students in class who used different amounts of solutions. Reflection and Revision What data should be used to compare temperatures in different experiments? How reproducible is this experiment? How could the experiment be changed to reduce the variability? What is the pattern between volumes of solution used and highest temperature reached? How can the experiment be changed to standardize this data? Write the chemical equation for this reaction. What does the data tell about the reaction between and acid and a base?	Levels of Performance
	Stage 4	Student work is complete, correct and shows detailed evidence of understanding the distinction between temperature, heat and the measurement of heat emitted from a chemical reaction. Measurements and observations are detailed and interpreted with logical reasoning. Discussion indicates understanding of the principle that the energy emitted in a chemical reaction is proportional to amount of reaction occurring and the need to establish correct ratios based on volumes and concentrations of the reactants.
	Stage 3	Student work is mostly complete and shows some evidence of understanding the distinction between temperature, heat and the measurement of heat emitted from a chemical reaction. Measurements and observations are interpreted with logical reasoning. Discussion indicates understanding of the principle that energy emitted in a chemical reaction is proportional to the amount of reaction occurring.
	Stage 2	Student work may be incomplete and shows limited understanding of distinction between temperature, heat or the measurement of heat emitted from a chemical reaction. Measurements and observations lack detail and the interpretation and discussion may show errors of reasoning.
	Stage 1	Student work is mostly incomplete and contains misconceptions relating to temperature, heat and the measurement of heat emitted from a chemical reaction. Measurements, observations, interpretations and discussion, if present, are minimal, and show a lack of scientific reasoning.

Standards Cross-References
( Alaska Department of Education & Early Development Standards)

National Science Education Standards

The nuclear forces that hold the nucleus of an atom together, at nuclear distances, are usually stronger than the electric forces that would make it fly apart. Nuclear reactions convert a fraction of the mass of interacting particles into energy, and they can release much greater amounts of energy than atomic interactions. Fission is the splitting of a large nucleus into smaller pieces. Fusion is the joining of two nuclei at extremely high temperature and pressure, and is the process responsible for the energy of the sun and other stars. (Page 178)

Radioactive isotopes are unstable and undergo spontaneous nuclear reactions, emitting particles and/or wavelike radiation. The decay of any one nucleus cannot be predicted, but a large group of identical nuclei decay at a predictable rate. This predictability can be used to estimate the age of materials that contain radioactive isotopes. (Page 178)

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. (Page 179)

Chemical reactions may release or consume energy. Some reactions such as the burning 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. (Page 179)

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. (Page 179)

Chemical reactions can take place in time periods ranging from the few femptoseconds (10–15 seconds) required for an atom to move a fraction of a chemical bond distance to geologic time scales of billions of years. Reaction rates depend on how often the reacting atoms and molecules encounter one another, on the temperature, and on the properties—including shape—of the reacting species. (Page 179)

Catalysts, such as metal surfaces, accelerate chemical reactions. Chemical reactions in living systems are catalyzed by protein molecules called enzymes. (Page 179)

The total energy of the universe is constant. Energy can be transferred by collisions in chemical and nuclear reactions, by light waves and other radiations, and in many other ways. However, it can never be destroyed. As these transfers occur, the matter involved becomes steadily less ordered. (Page 180)

Benchmarks

Atoms often join with one another in various combinations in distinct molecules or in repeating three-dimensional crystal patterns. An enormous variety of biological, chemical, and physical phenomena can be explained by changes in the arrangement and motion of atoms and molecules. (Page 80)

The configuration of atoms in a molecule determines the molecule’s properties. Shapes are particularly important in how large molecules interact with others. (Page 80)

The rate of reactions among atoms and molecules depends on how often they encounter one another, which is affected by the concentration, pressure, and temperature of the reacting materials. Some atoms and molecules are highly effective in encouraging the interaction of others. (Page 80)

Different energy levels are associated with different configurations of atoms and molecules. Some changes of configuration require an input of energy whereas others release energy. (Page 86)

When energy of an isolated atom or molecule changes, it does so in a definite jump from one value to another, with no possible values in between. The change in energy occurs when radiation is absorbed or emitted, so the radiation also has distinct energy values. As a result, the light emitted or absorbed by separate atoms or molecules (as in gas) can be used to identify what the substance is. (Page 86)

Energy is released whenever the nuclei of very heavy atoms, such as uranium or plutonium, split into middle weight ones, or when very light nuclei, such as those of hydrogen and helium, combine into heavier ones. The energy released in each nuclear reaction is very much greater than the energy given off in each chemical reaction. (Page 86)

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