Science Assessment

Students should know that:

1. The amount of chemical energy in a chemical reaction system before and after the reaction occurs depends on the types and number of atoms in the system and how they are arranged in molecules. Different systems of reactants and products typically have different amounts of chemical energy because they have different configurations of atoms.  
2. All chemical reactions involve both bond breaking and bond forming. Energy is always required to separate the atoms that make up molecules (bond breaking), and energy is always released when atoms connect to form molecules (bond forming). 
3. The relative amounts of energy required to break bonds and released when bonds are formed determines whether energy is given off to or taken in from the surroundings during a chemical reaction.
   1. For exothermic chemical reactions (reactions that release more energy than they take in), the amount of energy released as the product molecules form is greater than the energy required to separate the atoms of the reactant molecules. The energy transferred to the surroundings can be manifest as an increase in thermal energy or motion energy or the production of light or sound.
   2. For endothermic chemical reactions (reactions that take in more energy than they release), the amount of energy released as the product molecules form is less than the energy required to separate the atoms of the reactant molecules. The energy transferred from the surroundings can be detected by a decrease in temperature of the surroundings or the absorption of light or sound.
4. If energy is released during a chemical reaction, then the reverse reaction takes in energy [but the reverse reaction is not always possible]. If energy is taken in during a chemical reaction, then the reverse reaction releases energy (e.g., photosynthesis and cellular respiration).

Boundaries:

1. Students are not assessed on the definitions of the words “endothermic” and “exothermic.”
2. Students are not expected to know that the energy that can be released from or absorbed by  the reactants in a chemical reaction depends on other conditions such as temperature or type of solvent.
3. Students are not expected to quantify how much chemical energy is stored in any particular chemical reaction system. Students are not expected to know or use formulas associated with chemical potential energy.  The sub-ideas above describe semi-quantitative relationships.