Chemistry Unit 2

Unit Overview – Conservation

The big picture stuff:

In middle school, students are introduced to chemical vs. physical changes and balancing simple equations, however this unit provides the mathematical basis behind predicting what will happen during a chemical reaction. Students are also given more autonomy in making decisions on quality experimental design.

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: the idea that a chemical reaction is a system that affects the energy change.

Examples of models include molecular-level drawings and diagrams of reactions, graphs showing the relative energies of reactants and products, and representations showing energy is conserved.

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.

PS1-7. Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.

Emphasize: use mathematical ideas to communicate the proportional relationships between masses of atoms in the reactants and the products, and the translate these relationships to the macroscopic scale using the mole as the conversion from the atomic to the macroscopic scale. Focus on assessing students’ use of mathematical thinking and not on memorization and rote application of problem-solving techniques.

Core ideas: The fact that atoms are conserved, together with knowledge of the chemical properties of the elements involved, can be used to describe and predict chemical reactions.

Science and Engineering:

• Use mathematical representations of phenomena to support claims.
• Develop a model based on evidence to illustrate the relationships between systems or between components of a system.

Crosscutting concepts:

• 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.
• Science assumes the universe is a vast single system in which basic laws are consistent.
• The total amount of energy and matter in closed systems is conserved.

California Science Standards – Chemistry

3a. Students know how to describe chemical reactions by writing balanced equations.

3b. Students know the quantity one mole is set by defining one mole of carbon 12 atoms to have a mass of exactly 12 grams.

3c. Students know one mole equals 6.02Ê´Ê1023 particles (atoms or molecules).

3d. Students know how to determine the molar mass of a molecule from its chemical formula and a table of atomic masses and how to convert the mass of a molecular substance to moles, number of particles, or volume of gas at standard temperature and pressure.

3e. Students know how to calculate the masses of reactants and products in a chemical reaction from the mass of one of the reactants or products and the relevant atomic masses.

Investigation and Experimentation Standards:

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.