Unit 10A - Heat and Thermochemistry - AP Chemistry

system

system

the region being considered in a problem

surroundings

everything that is outside of the system

heat

the total amount of thermal (kinetic) energy held by the system

units = J, kJ, or cal

temperature

the average thermal (kinetic) energy held by the molecules of the system

units = degrees Celsius or Kelvin

endothermic

heat energy is taken in by the system (feels cold to you, the surroundings)

exothermic

heat is energy is released by the system (feels hot to you, the surroundings)

“positive” heat of a reaction (+q)

heat flows in to the reaction

heat is being pulled out of the surroundings and the temp goes down

“negative” heat of a reaction (-q)

heat flows out of the reaction

heat is being released into the surroundings and the temp goes up

measuring the change in temperature of a solution during dissolving or other physical changes

tells whether or not and how much energy was required/released for that process to occur

measuring the temperature change of a system due to a chemical reaction

tells the amount of energy given off or absorbed during the reaction

equation for quantifying heat energy

specific heat capacity

a measure of the amount of heat energy required to raise the temperature of 1 gram of a substance 1 degree Celsius

Cp

specific heat capacity measured at constant pressure

for gases, this means the measurement was taken allowing the gas to expand as it was heated

Cv

specific heat capacity measured at constant volume

for gases, this means the measurement was made in a sealed container, allowing the pressure to rise as the gas was heated

calorimetry

the measurement of heat flow

calorimeter

an insulated container for performing reactions that involve measuring heat

coffee cup calorimeter

a calorimeter that is only an insulated container - often containing your system (reactants) dissolved directly in water

can be made from a styrofoam coffee cup

bomb calorimeter

a calorimeter for measuring the heat produced by a chemical reaction

the calorimeter contains a mass of water

the heat from the reaction makes the temp of the water change

calorimeter equation