A constant-pressure calorimeter measures the change in enthalpy of a reaction occurring in solution during which the atmospheric pressure remains constant.
Since pressure is constant, the change in enthalpy is equal to heat (

An example of a constant-pressure calorimeter is a coffee-cup calorimeter, which is constructed from two nested Styrofoam cups and a lid with two holes, which allows for the insertion of a thermometer and a stirring rod. The inner cup holds a known amount of a liquid, usually water, that absorbs the heat from the reaction. The outer cup is assumed to be perfectly adiabatic, meaning that it does not absorb any heat whatsoever. As such, the outer cup is assumed to be a perfect insulator.

## Calculating Specific Heat

Data collected during a constant-pressure calorimetry experiment can be used to calculate the heat capacity of an unknown substance. We already know our equation relating heat and heat capacity:

Now, let's use this equation to calculate specific heat.

### Example:

A student heats a 5.0 g sample of an unknown metal to a temperature of 207

The walls of the coffee-cup calorimeter are assumed to be perfectly adiabatic, so we can assume that all of the heat from the metal was transferred to the water:

Substituting in our above equation, we get:

Then we can plug in our known values:

The specific heat of the unknown metal is 0.166