Chemistry Unit 5

Unit Overview – Heat and Thermodynamics

The big picture stuff:

While the ideas of heat and temperature, including endothermic and exothermic reactions are introduced in middle school, high school allows students to predict the type of reaction that occurs based on calculations. At this stage, students explore the difference between heat and temperature, the difference between latent and specific heat, and the relationship between the amount of energy released and the strength of the chemical bonds.

Next Generation Science Standards – High School (NGSS-HS):

PS1-4. Develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy.

Emphasize: a chemical reaction is a system that affects the energy change. Examples of models could include graphs showing the relative energies of reactants and products, and representations showing energy is conserved. Do not include calculating the total bond energy changes during a chemical reaction from the bond energies of reactants and products.

Core ideas: Stable forms of matter are those in which the electric and magnetic field energy is minimized. A stable molecule has less energy than the same set of atoms separated; one must provide at least this energy in order to take the molecule apart.

PS1-5. Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs.

Emphasize: student reasoning that focuses on the number and energy of collisions between molecules. Focus on simple reactions in which there are only two reactants; evidence from temperature, concentration, and rate data; and qualitative relationships between rate and temperature.

Core ideas: Chemical processes, their rates, and whether or not energy is stored or released can be understood in terms of the collisions of molecules and the rearrangements of atoms into new molecules, with consequent changes in the sum of all bond energies in the set of molecules that are matched by changes in kinetic energy.

PS3-2. Develop and use models to illustrate that energy at the macroscopic scale can be accounted for as either motions of particles or energy stored in fields.

Examples: the conversion of kinetic energy to thermal energy. Models could include diagrams, drawings, descriptions, and computer simulations.

Core ideas: Energy is a quantitative property of a system that depends on the motion and interactions of matter and radiation within that system. That there is a single quantity called energy is due to the fact that a system’s total energy is conserved, even as, within the system, energy is continually transferred from one object to another and between its various possible forms. At the macroscopic scale, energy manifests itself in multiple ways, such as thermal energy.

PS3-4. Plan and conduct an investigation to provide evidence that the transfer of thermal energy when two components of different temperature are combined within a closed system results in a more uniform energy distribution among the components in the system (second law of thermodynamics).

Emphasize: Analyze data from student investigations and use mathematical thinking to describe the energy changes both quantitatively and conceptually. Examples of investigations could include mixing liquids at different initial temperatures or adding objects at different temperatures to water.

Core ideas: Although energy cannot be destroyed, it can be transported from one place to another, transferred between systems , and converted to less useful forms—for example, to thermal energy in the surrounding environment.Uncontrolled systems always evolve toward more stable states—that is, toward more uniform energy distribution.

Science and Engineering:

• Apply scientific principles and evidence to provide an explanation of phenomena and solve design problems, taking into account possible unanticipated effects.
• Develop and use a model based on evidence to illustrate the relationships between systems or between components of a system.
• Plan and conduct an investigation individually and collaboratively to produce data to serve as the basis for evidence, and in the design: decide on types, how much, and accuracy of data needed to produce reliable measurements and consider limitations on the precision of the data (e.g., number of trials, cost, risk, time), and refine the design accordingly.

Crosscutting concepts:

• Different patterns may be observed at each of the scales at which a system is studied and can provide evidence for causality in explanations of phenomena.
• Changes of energy and matter in a system can be described in terms of energy and matter flows into, out of, and within that system.
• When investigating or describing a system, the boundaries and initial conditions of the system need to be defined and their inputs and outputs analyzed and described using models.
• Energy cannot be created or destroyed—only moves between one place and another place, between objects and/or fields, or between systems.

California Science Standards – Chemistry

7a. Students know how to describe temperature and heat flow in terms of the motion of molecules (or atoms).

7b. Students know chemical processes can either release (exothermic) or absorb (endothermic) thermal energy.

7c. Students know energy is released when a material condenses or freezes and is absorbed when a material evaporates or melts.

7d. Students know how to solve problems involving heat flow and temperature changes, using known values of specific heat and latent heat of phase change.

7e.* Students know how to apply Hess’s law to calculate enthalpy change in a reaction.

Investigation and Experimentation Standards:

a. Select and use appropriate tools and technology (such as computer-linked probes, spreadsheets, and graphing calculators) to perform tests, collect data, analyze relationships, and display data.

b. Identify and communicate sources of unavoidable experimental error.

c. Identify possible reasons for inconsistent results, such as sources of error or uncontrolled conditions.

d. Formulate explanations by using logic and evidence.

e. Solve scientific problems by using quadratic equations and simple trigonometric, exponential, and logarithmic functions.

g. Recognize the usefulness and limitations of models and theories as scientific representations of reality.

j. Recognize the issues of statistical variability and the need for controlled tests.

k. Recognize the cumulative nature of scientific evidence.

l. Analyze situations and solve problems that require combining and applying concepts from more than one area of science.