1. Chapter 12 ENERGY
REVIEW OF MAIN TOPICS

2. 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

3. 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

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

5. 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

6. Enthalpy (delta H) calculations
Propane (C3H8) + 5 O2 yields 3CO2 + 4 H Delta H = 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