2. Key Terms Average kinetic energy - Energy associated with the movement of matter and mass Bond energy - The amount of energy it takes to break one mole of bonds Calorimetry - measurement of quantities of heat Chemical energy - the energy in a substance that can be released by a chemical reaction Collision theory - explains how chemical reactions occur and why reaction rates differ for different reactions Delta H (ΔH) - a measure of the energy associated with a system Endothermic - Requiring a net input of heat for its formation Enthalpy - a measure of the energy associated with a system

3. Key Terms Exothermic - Accompanied by the release of heat Heat - a form of energy that is transferred by a difference in temperature Molecular movement - how molecules move and is measured by temperature Potential energy diagram - plots the change in potential energy that occurs during a chemical reaction Specific heat - The heat required to raise the temperature of the unit mass of a given substance by a given amount Temperature - The measure of molecular motion or the degree of heat of a substance Thermal energy - The total potential and kinetic energy associated with the random motions of the molecules of a material

4. Types of Energy Mechanical Kinetic – based on particle motion Potential – based on height and acceleration due to gravity Chemical Kinetic – based on particle motion to define temperature Equation: KE=1/2 MV 2 Potential – energy stored in chemical bonds Electrical – based on the flow of electrons from an area of high charge to an area of low charge Nuclear – based on the release of energy stored in the nucleus Thermal – based on the transfer of heat

5. Energy Transfer Energy always flows from a position of high energy to a position of low energy There are multiple ways that energy is transferred Potential to Kinetic as objects fall Kinetic to potential as objects rise Electrical Chemical as reactions occur Thermal from hot to cold (energy cannot be transferred from cold to hot)

6. Chemical Energy Transfer The chemical energy transferred in chemical reactions is related to the difference in potential energy of the reactants and the products The potential energy of chemical compounds is stored in the compounds when they are formed – the heat of formation (H f o ) We standardize the heats of formation based on the difference found when the compounds are formed from elements. This means that the heat of formation of any element always equals zero

7. Enthalpy & Types of Reactions When thermal energy leaves the reaction, the reaction is called exothermic ∆H RXN is negative – thermal energy is leaving the system Potential energy of products is less than the potential energy of the reactants It is the excess potential energy of the reactants that is leaving as thermal energy When thermal energy comes into the reaction, the reaction is called endothermic ∆H RXN is positive – thermal energy is entering the system Potential energy of products is greater than the potential energy of the reactants It is the thermal energy entering the system that provides the additional potential energy needed to form the products.

8. Reaction Coordinate Diagrams for Endothermic & Exothermic Reactions Energy of Reactants < Energy of Products Endothermic Energy of Products < Energy of Reactants Exothermic ΔH RXN = ΔH Products - ΔH Reactants

9. Heat of Reaction - Enthalpy The heat transfer in a chemical reaction is defined as enthalpy which r epresents the change in the energy stored in the chemical bonds The Enthalpy is equal to the overall change in chemical potential energy: ∆H RXN Enthalpy = Potential Energy of Products – Potential Energy of Reactants ∆H RXN = ∑ ∆H f 0 (products) - ∑ ∆H f 0 (reactants)

10. Law of Conservation of Energy Energy may not be created or destroyed Energy may change form Therefore, the sum of all of the energies in a system is a constant Enthalpy = Potential Energy of Products – Potential Energy of Reactants ∆H RXN = ∑ ∆H f 0 (products) - ∑ ∆H f 0 (reactants) ∆H RXN is positive, the reaction is endothermic ∆H RXN is negative, the reaction is exothermic

11. Specific Heat & Calorimetry The heat of reaction is measured through a process of determining the effect on the environment. Assuming no loss of energy, the energy out of one system is equal to the gain in energy of another system. Calorimetry is the process of quantifying this energy Calorimetry is dependent on knowing the effect of temperature change on the environment – specific heat

12. Specific Heat Specific Heat (c p ) - The amount of thermal energy (heat) required to change the temperature of one gram of matter, one degree Celsius. The use of specific heat allows for determining the amount of heat lost or gained. Heat gained or lost = (mass) (specific heat) (change in temperature) q = m c p ΔT

13. Heating Curve of Water Image used courtesy of http://ch301.cm.utexas.edu/thermo/selector.php?name=heat-curves

14. Calorimetry Assuming no loss of heat, the thermal energy out of one system is equal to the gain in thermal energy of another system. q in = - q out If q out = ∆H RXN, then q in = - ∆H RXN If enthalpy is negative, temperature increases (exothermic) If enthalpy is positive, temperature decreases (endothermic)