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Tips on Understanding the Difference Between Calorimeters - Concept

Teacher/Instructor Kendal Orenstein
Kendal Orenstein

Rutger's University
M.Ed., Columbia Teachers College

Kendal founded an academic coaching company in Washington D.C. and teaches in local area schools. In her spare time she loves to explore new places.

Tips on understanding the difference between a coffee cup calorimeter and a bomb calorimeter.

A calorimeter is a reaction vessel that actually helps us identify the enthalpy change in a particular reaction. So we have coffee cup calorimeter on our left hand side, and a drawing of a bomb calorimeter on our right hand side. Let's start off with the coffee cup calorimeter.

The coffee cup calorimeter is made of styraphoam. That's one major difference. Bomb calorimeters is made of metal. Serious difference. So what happens is, this is like they both closed top. We put a reaction in the water. The water acts as our solvent for the reaction. So we put into our solutions, see how they they react and see if there is exothermic or endothermic. And if the water heats up it's measured by the thermometer on the left hand side and the change in temperature of the water, is equal to the amount of energy released from the reaction.

So we can basically say how much energy is released from the reaction, and 'q', this is the notation for energy released or heat released from the reaction is equal to the heat gained by the water. And we're assuming this is an exothermic. It could be endothermic and then the signs would be different. So we can also say that and be more specific, mc delta T of the reaction is equal to mc delta T of the water. And if there is negative on the reaction side that means temperature is going down, if it is negative in the water side and if the temperature of the water is going down it really depends on if its exo/endothermic for that negative sign ends up.

But basically saying the amount of energy released is the amount of energy gained and assuming no loss of heat to the surrounding. We do basically assume that they come to one level. This is great, it's very simple, it's not complex at all just as a reaction takes place, water will heat up and you can measure how much energy that is.

If we have a bomb calorimeter, it's not a true bomb. It's made of metal. We have this reaction vessel inside, and that's where the reaction takes place. And that heats up this metal in casing and then the metal in casing therefore then heats up the water and we compare the amount of energy that the metal in casing, or we call the bomb, heats up the water is the amount of energy released from the reaction inside. So another way of saying this is q of the reaction is equal to the negative, again it's exothermic, q of the water plus q of the bomb.

So we're going to heat up with this reaction that is taking place in here, is going to heat this up and then this is going to heat up the water. A little bit different than the coffee cup calorimeter. We can also say q of the bomb is equal to c delta t. And c is heat capacity and that the heat capacity is specific heat times mass. So cm, because these are constants for each bomb calorimeter.

The specific heat for this metal is not going to change as long as we don't change the bomb calorimeter. And the mass of this reaction is not going to change either, as long as we continue to use this particular bomb calorimeter. This is unique, this heat capacity is unique for each calorimeter.

So we can basically measure the heat given off by measurement and how much that water heats up from the gas chamber. Now why would you I a bomb calorimeter over a coffee cup calorimeter? Well there are several things. Coffee cup calorimeter is much easier and probably used much often than a bomb calorimeter. But bomb calorimeter is also used in high temperature reactions for processes. High temperature reactions because a styraphoam container is going to melt in high temperature, so we're not going to use that in high temperatures. We're going to use a bomb calorimeter for high temperatures. We're also going to use it for gas reactions; reactions that produce gases because if we have reactions producing gases in our coffee cup calorimeter, that's not going to work very well because it is just measuring the change in the liquid. So that's not going to work at all, the gases will escape and it's going to mess up our whole data.

In the metal,calorimeter the gases are contained within this bomb situation, and so therefore it is measured accurately. So gas reactions when you use bomb calorimeters.

So hopeful that helps you understand the difference between coffee cup calorimeters and bomb calorimeters. They are both used actually quite often. They are both pretty accurate ways of deciding the delta H or the enthalpy of a particular reaction, or how much energy is given off by a particular reaction, or a process. Hopefully that helped.