Heat energy equation
q = mCp (Triangle T)
unit for q
Joules (SI unit for heat) or calories
calorie (cal)
this is the more well known unit for heat. It is the amount of heat required to raise temp of 1 g of H2O by 1 degree Celsius.
1 Calorie (Capital & underlined)
1000 calories
1 calorie
4.184 J
q =
heat energy lost or gained (J)
m =
mass (g) or ml
Cp =
specific heat (J/g degree Celsius)
triangle T =
difference in initial and final temperature in C
Specific heat define
amount of energy needed to raise temperature of 1 g of substance by 1 degree Celsius. e.g. for water: 4.184 J/g C. It is measured under constant pressure, so symbol is Cp. Unit are in: J/g C. Specific pressure is unique to the substance. It is an intensive property. Bc it's always the same.
q and triangle H
both show energy either released or absorbed. triangle H rxn is used for chemical reactions, and q is used for all chemical and physical processes involving heat transfer under constant pressure. Since most reactions occur under constant pressure, q = triangle H rxn.
When q is positive energy is absorbed.
When q is negative energy is released.
We use calorimetry
to calculate how much heat is absorbed or released in a chemical reaction. It is a method to determine heat involved in a physical or chemical change. Relies on the law of conservation of energy.
Calorimeter
insulated device used to measure amount of heat lost or gained by a chemical reaction or even a physical process. It works by measuring the temperature change in the water surrounding it. In a calorimetry experiment, heat is absorbed by water in the calorimeter should be equal to the heat lost by the sample. We write this as: q calorimeter (mCp triangle T) = - q sample (mCp triangle T)