Equations
What is the equation for total energy?
change in energy = q + w
where q is heat and w is work
Define exothermic reactions. Define endothermic reactions.
Exothermic reaction: release heat energy
Endothermic reaction: absorb heat energy
What does calorimetry measure?
measures the amount of heat transferred in a chemical reaction
What is the equation for the first law of thermodynamics?
change in energy of the system = - change in energy of the surroundings
Exothermic reactions release heat energy, so is q positive or negative?
negative
Which relationship is important to remember for constant volume calorimetry?
qCal = -qsample
heat gained by calorimeter equals heat lost by sample
What is the equation for heat capacity? What is the unit for each variable?
C = q/change in T
where C is heat capacity (J/degrees Celsius), q is heat (joules), and T is temperature (Celsius)
Endothermic reactions absorb energy, so is q positive or negative?
positive
Which relationship is important to remember in constant pressure calorimetry?
qsolution = -qreaction
heat gained by solution equals heat lost by reaction
What is the equation for specific heat? What is the unit of each variable?
Cs = q/(m x change in T)
where Cs is specific heat (J/g x degrees Celsius), q is heat (joules), m is mass (grams), and T is temperature (Celsius)
When a system uses energy to do work on surroundings, is w positive or negative?
negative
What happens in constant pressure calorimetry?
also called coffee cup calorimetry
1. a known amount of water is placed in an insulated cup
2. system to be studied is placed in water and allowed to react
3. temperature change is recorded
What is specific heat? What is heat capacity?
specific heat: the amount of energy required to raise 1 gram of material by 1 degree Celsius
heat capacity: amount of heat required to raise the total mass by 1 degree Celsius
When a system gains energy from action of the surroundings, is w positive or negative?
positive
What happens in constant volume calorimetry?
also called bomb calorimetry
1. a test sample is placed in a heavy steel container
2. steel container is placed within a water bath
3. ignition wire detonates the sample
4. temperature change of water bath is recorded