A calorimeter is a device in which one can measure and calculate or predict different properties of certain substances. While there are very expensive calorimeters out there, you can make one with a styrofoam cup of cool water.
The expression used in calorimeter problems is:
m * Cp * ΔT = m * Cp * ΔT
ΔT is |Tf - Ti|
What this all means:
- m: mass
- Cp: Specific heat: The amount of energy (in Joules) required to raise 1 gram of the specified substance 1 degree Celsius. The specific heat of liquid water is 4.18 J/(g*°C)
- ΔT: Change in temperature: the absolute value of the final temperature - the initial temperature
Calorimeter problems are sometimes rounded to two digits after the decimal point no matter how many significant digits are present in the problem due to the fact that the change in temperature of the system can be very small.