Mr. Quinn & Ms. Tom February 28, 2014 Aim: How do we measure energy changes in a chemical reaction? Do Now: Identify the term for a reaction where the products have more energy than the reactants. Identify the term for a reaction where the reactants have more energy than the products.

Endothermic Reactions Two Types of Reactions Exothermic Reactions Temperature increases Energy is released Heat is a product Endothermic Reactions Temperature decreases Energy is absorbed Heat is a reactant

Energy changes can be expressed quantitatively What does that mean???

Quantitative energy levels for EXOTHERMIC REACTION Activation Energy: Heat of Reaction:

Quantitative energy levels for ENDOTHERMIC REACTION Activation Energy: Heat of Reaction:

Let’s Try It Out! According to Reference Table I, the dissolving of NH4Cl (s) in water is exothermic and the heat of reaction is negative exothermic and the heat of reaction is positive endothermic and the heat of reaction is negative endothermic and the heat of reaction is positive Given the equation: I + I → I2 + 35 kcal This equation shows that the formation of an iodine molecule is an exothermic process in which energy is absorbed exothermic process in which energy is released endothermic process in which energy is absorbed endothermic process in which energy is released

Let’s Try It Out! Which statement correctly describes the energy changes that occur in the forward reaction? The activation energy is 10. kJ and the reaction is endothermic. The activation energy is 10. kJ and the reaction is exothermic. The activation energy is 50. kJ and the reaction is endothermic. The activation energy is 50. kJ and the reaction is exothermic.

Your Turn!

Your Turn! According to Reference Table I, what is the heat of reaction for the formation of two moles of H2O(l) from hydrogen and oxygen gas at 1 atmosphere and 298 K? –571.6 kJ –483.6 kJ –55.8 kJ +571.6 kJ Which change of phase is exothermic? H2O(s) → H2O(g) CO2(s) → CO2(l) H2S(g) → H2S(l) NH3(l) → NH3(g)

Your Turn! When an exothermic reaction occurs in a water solution, the temperature of the solution increases because energy is given off by the reaction increases because energy is absorbed by the reaction decreases because energy is given off by the reaction decreases because energy is absorbed by the reaction In a chemical reaction, the difference between the potential energy of the products and the potential energy of the reactants is the heat of reaction heat of fusion free energy activation energy