 What is the formula for finding heat?

 What are the two units of heat?

 The temperature of a sample of iron with a mass of 10.0 g changed from 50.4 o C to 25.0 o C. If the specific heat of iron is 0.449 J/g x o C, how much heat was released?  A 4.50 g nugget of pure gold absorbed 276 J of heat. What was the final temperature of the gold if the initial temperature was 25 o C? The specific heat of gold is 0.129 J/(g x o C).

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 Calorimeter  Uses insulated material to measure heat absorbed or released.

 Usually has water in it  Can determine specific heats  Whatever heat is gained by the water, it is lost by the substance in the water

 Thermochemistry- study of heat changes that accompany chemical reactions and phase changes  Two parts are changing in a reaction  system and surroundings  Universe = system + surroundings  Ex. Hand warmers  If exothermic, heat is a product  If endothermic, heat is a reactant

       the heat content of a system at constant pressure Cant actually measure the actual energy or enthalpy of a substance but you can measure change ΔH rxn = H products – H reactants Exothermic = negative (released to the surroundings) Endothermic (absorbed by the system) = postive Written: 4Fe + 3O 2  4Fe + 3O 2  2Fe 2 O 3 q= ΔH rxn  2Fe 2 O 3 ΔH rxn + 1625 kJ = -1625 kJ

 Can not just rely on exo and endo to tell   Ex. CH 4 +2O 2  CO 2 + H 2 O ΔH rxn = -891 kJ Molecules would rather exists in a high state of disorder (called entropy)  Second law of thermodynamics  entropy in spontaneous process will always increase  Entropy = ΔS (products – reactants)  If entropy increases, ΔS is positive  Ex. Water changing from solid to liquid to gas  Ex. Decrease in temperature

 Can use the Gibbs free energy equation to determine if a reaction will be spontaneous   ΔG system = ΔH system – TΔS system Temp in Kelvin, H in Joules  If G is negative- reaction is spontaneous  If G is positive- reaction is nonspontaneous  Ex. For a process, ΔH sys = 145 kJ and ΔS sys = 322 J/K. Is the process spontaneous at 382 K?

 Determine if the following process is spontaneous or nonspontaneous:  ΔH sys = -75.9 kJ, T = 273 K, ΔS sys = 138 J/K  Is it an endothermic reaction or exothermic?

  Atoms, ions, and molecules must collide in order to react Only a small fraction of particles actually collide     Must collide in the correct orientation Once they collide, they make an intermediate molecule called an activated complex  exist in the transition state Must also have the right amount of energy (called activation energy) If a reaction has a high E a , few collision  low E a , high collisions

 Exothermic- molecules collide with enough energy to overcome the E a and produce products at a lower energy level  Endothermic- reactants lie at a low energy level and must absorb energy to overcome the E a .