Note Guide 7-4 Branch of chemistry that studies energy changes which take place during reactions and changes in state of matter = thermochemistry Potential energy = energy of position/stored energy. But in chemistry we have chemical potential energy = energy stored in the chemical bonds of a substance --how much energy stored is determined by kinds of atoms and how they are arranged. Heat(q) = energy that transfers from one object to another due to a difference in temperature between them --how does heat transfer? From the WARMER to the COLDER OBJECT

Law of conservation of energy =matter will neither be created nor destroyed, including chemical processes. --this means if a system gives off heat (loses), it must go somewhere, therefore it goes into the surrounding area of the system. --2 Process 1.Endothermic – system gains heat as the surroundings cool off. --heat is absorbed EX: the person is absorbing the heat given off

2. Exothermic – system loses heat as the surroundings heat up --giving off heat. EX: the body (system) loses heat to the surroundings (skin/air)— sweat/perspire Heat movement is measured 2 ways 1. Calories – quantity of heat needed to raise the temp. of 1 g of pure water 1 deg. C 2. Joule – SI unit of energy.

Heat capacity = how much heat is needed to raise the temp of an object 1 deg C. --depends on. a.Mass – more mass of the object, more heat it can hold b.Chemical make-up – different substance can have diff. Heat capacity even though mass may be equal. --of course, we cant call it just heat capacity, we have to change the name = specific heat capacity --amount of heat needed to raise the temp of 1 g of the stuff 1 deg C. --COPY FORMULA FROM PAGE 509

7-4 Note Guide, part deux Enthalpy = heat content of a system at constant pressure In a chemical reaction, the enthalpy change for the reaction can be written as either a reactant or a product. --calcium oxide and water react as an exothermic reaction CaO(s) + H 2 O(l)  Ca(OH) 2 (s) kJ --heats of reaction usually shown as ΔH Heat of reaction = enthalpy change for the chemical equation exactly as it is written CaO(s) + H 2 O(l)  Ca(OH) 2 (s) ΔH =-65.2kJ

--other reactions are endothermic. Baking soda decomposes when heated 2NaHCO 3 (s) kJ  Na 2 CO 3 (s) +H 2 O(g) + CO 2 (g) ΔH=129kJ --The amount of heat released or absorbed during a reaction depends on the number of moles of the reactants invovled Pg. 516 Sample problem 17.3 Heat of combustion = heat of reaction for the complete burning of one mole of a substance.

Normally, the actual yield in a chemical reaction will be equal to or less than the theoretical yield. 1.Always True 2.Sometimes True 3.Never True

The amount of product can be determined from the amount of excess reagent. 1.Always True 2.Sometimes True 3.Never True

What would likely happen if you were to touch the flask in which an endothermic reaction were occuring? 1.The flask would probably feel cooler than before the reaction started. 2.The flask would probably feel warmer than before the reaction started. 3.The flask would feel the same as before the reaction started. 4.None of the above

What does the symbol ΔH stand for? 1.The specific heat of a substance 2.The heat capacity of a substance 3.The heat of reaction for a chem. reaction 4.One Calorie given off by a reaction

The amount of heat released by the complete burning of 1 mol of a substance is the 1.Specific heat 2.Heat of combustion 3.Heat capacity 4.Heat of fusion.