A calorimeter is a tool that measures the amount of heat flow in a chemical reaction. There are two popular calorimeters which include a bomb calorimeter and a coffee cup calorimeter.
The Basic Coffee Cup Calorimeter
A coffee cup calorimeter is basically made of polystyrene. It is also a Styrofoam cup that has a cover. It is simply one cup inside another with a cover to give insulation to the content mixed in it. For a basic coffee cup calorimeter, a Styrofoam insulator and a sensitive thermometer completes the device. A more complex machine will have a Dewar flask, a double-walled container that has reduced pressure in between the two walls.
Measure some amount of water, partially fill the cup, cover it, and insert a thermometer through the cup’s lid until the bulb is below the water surface. Any chemical reaction that takes place inside the coffee cup calorimeter, leads to production of heat, which the water absorbs. The chemical process leads to heat emission that alters the water temperatures. The variations in the levels of water temperature helps to show the amount of heat that is required in any coffee extraction process. It also shows the amount of heat lost to the water when the temperature increases during the process.
To get the amount of heat flow use the following equation:
q = (specific heat) x m x Δt
q is heat flow
m is mass in grams
Δt is the change in temperature.
Specific heat shows the amount of heat needed to change the amount of heat of one gram of a substance per 1oC. The standard measure of heat of water equivalent to 4.18 J/(g·°C).
For instance, if you carry out a chemical reaction using 100 grams of water with a starting heat of 20.0 C. let the reaction take place in the coffee cup calorimeter, and observe the temperature changes. After the chemical process, there is an increase in temperature to 26.0 C. You will get the amount of heat flow by:
qwater = 4.18 J/(g·°C) x 100 g x (26.0 C – 20.0 C)
qwater = +2.5 x 103 J
The products of the reaction produced 2,500 J of heat, which the water absorbed. An enthalpy change, ΔH, arising from the process is same in terms of the figure but has a different sign with the water’s heat flow:
ΔHreaction = -(qwater)
When it comes to exothermic reactions, ΔH < 0, qwater is positive. The water absorbs heat emitted from the reaction, and there is a visible rise in temperature. When it comes to an endothermic reaction, the enthalpy change ΔH > 0, qwater is negative. In this reaction the water provides heat and this shows a reduction in temperature.