Chapter 12 ENERGY REVIEW OF MAIN TOPICS

Terminology Exothermic – reaction which gives off energy Endothermic – reaction which takes in energy Calorimeter – device used to calculate heat content of a food or fuel Specific Heat – amount of heat needed to raise one gram of a substance by one degree C Heat of combustion – amount of heat given off when a fuel or food burns Hess’s Law – states that if a series of reactions are added together, the overall enthalpy change for the net reaction is the sum of the enthalpy changes for the individual steps Heat – the transfer of kinetic energy from a hotter object to a cooler object – CALORIES, JOULES, kcal, kjoules Temperature – degrees C

Lab Review In lab we found the _____ of _________ of several fuels. The pop can acted as our ____________ and we assumed that all heat went directly from our fuel into the ____________ . We then used the formula _____________ to calculate the heat value for each fuel. Many groups had a high percent error because heat was lost to the ________ and the _________ and the _________ . heat of combustion calorimeter water H = m x s x T AIR CAN thermometer

Classify as EXO or ENDOthermic AB yields A + B + energy A + B + C + energy yields ABC AB yields A+ B + 113 Kj exothermic endothermic exothermic

Enthalpy Enthalpy is a big fancy word for heat gained or lost in a reaction. Signified by the letter delta H Delta H = H (products) – H(reactants) Delta H = + means ENDOTHERMIC Delta H = - means EXOTHERMIC

Enthalpy (delta H) calculations Propane (C3H8) + 5 O2 yields 3CO2 + 4 H20 Delta H = -2043 Kj This means that for EACH mole of propane you burn you will get 2043 Kjoules of heat given off. How much heat will be given off when you burn 3.5 GRAMS of propane… ? USE UNIT ANALYSIS !! 1 mole prop 2043 Kj 3.5 grams prop 162.5 Kj 44 grams prop 1 mole prop 1