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### Course: High school chemistry>Unit 6

Lesson 4: Calorimetry

# Constant-pressure calorimetry

Constant-pressure calorimetry is used to measure the change in enthalpy, ΔH, for a physical or chemical process. In this technique, a process is carried out in solution in a coffee cup calorimeter, an inexpensive device composed of two Styrofoam cups. The amount of heat transferred in the process (q) can be calculated from the mass, specific heat, and temperature change of the solution. Because the calorimeter is at constant (atmospheric) pressure, q is equal to ΔH for the process. Created by Jay.

## Want to join the conversation?

• At , due to the law of conservation of energy,should the energy in the system stay the same? Assuming that the system is reffering to the block and the water, the thermal energy in both objects should be the same before and after equillibrium, right?
• So the law of conservations of energy states that the energy of the universe is constant. And when we're talking about thermodynamics the universe is the system and the surroundings combined. So energy can leave the system and be transferred to the surroundings. So individually the system loses energy and the surroundings gain energy, but together the energy content is constant because they both constitute the universe.

In a chemistry context, the system refers to the reaction; specifically just the chemicals reacting. The water enveloping the block (the reaction) would be part of the surroundings. So the energies (and therefore temperatures) of the reaction and water (and technically the rest of the surroundings) will change over the course of the reaction, and this is still allowed under the law of conservation of energy because the sum of their energies remained constant.

Hope that helps.
• how did they come up with the name calorimeter?
• “Calor” is Latin for heat, and “metry” is Greek for measurement. So it literally means heat measurements.
• wait so when he's talking about constant pressure, he's talking about how the atmosphere around the system or whatever. So what does the pressure part really mean? Is it talking about how the atmosphere can absorb some of the heat or transfer heat?