Energy change that occurs during a chemical reaction and/or changes in state

 A form of energy  Flows from warmer objects to cooler objects  Represented by the variable “q”  Measured by units: calorie or joule 1 J = cal4.184 J = 1 cal 1000 cal = 1 kilorcalorie = 1 Cal

 Exothermic Process ◦ Energy flows from the system into the surroundings  Endothermic Process ◦ Energy flows from the surroundings into the system  Conservation of Energy ◦ Energy is not created or destroyed in a physical or chemical process ◦ If energy in a system decreases, then the energy of the surroundings increases by the same amount

 Amount of heat needed to increase the temperature of an object exactly 1 ˚C ◦ Depends on mass and chemical composition ◦ Greater mass = greater heat capacity  Specific Heat Capacity, C (Specific Heat) ◦ Amount of heat needed to raise 1 g of a substance by 1 ˚C ◦ Metals have low specific heats ◦ Water has a relatively high specific heat

 C = q / (m x ΔT)  C is the variable for specific heat ◦ Could be in units of J/(g ˚C) or cal/(g ˚C)  q is the variable for heat (joules or calories)  M is the variable for mass (grams)  ΔT (T f – T i ) is the variable for change in temperature (˚C) *become familiar with table 17.1 on page 508

 Enthalpy (H) is the heat content of a system at constant pressure ◦ Heat absorbed or released by a system (constant pressure) is the change in enthalpy, ΔH ◦ We will only work with a constant pressure scenario…therefore, q = ΔH  Calorimetry ◦ Measurement of heat flow into/out of a system ◦ Calorimeter is the device used to measure heat flow

 If a system gains heat, that amount of heat was lost by the surroundings…  q sys = - q surr (the negative sign represents loss)  ΔH = q sys = - q surr = - m x c x ΔT  Exothermic reactions have a negative value for ΔH  Endothermic reactions have a positive value for ΔH

 A chemical equation that includes enthalpy change  Can be either a “reactant” ◦ Endothermic 2NaHCO kJ  Na 2 CO 3 + H 2 O + CO 2 or 2NaHCO 3  Na 2 CO 3 + H 2 O + CO 2 ΔH = 129 kJ  Or a “product” ◦ Exothermic CaO + H2O  Ca(OH) kJ or CaO + H2O  Ca(OH)2 ΔH = kJ