Calorimetry

Calorimetry is the process of measuring the amount of heat released or absorbed during a chemical reaction. Calorimetry is a way of determining whether or not a reaction is exothermic, releases heat, or endothermic, absorbs heat. Calorimetry is a large aspect of thermodynamics, temperature measurements, because it gives the ability to collect data under specific conditions. Calorimetry is also a large part of everyday life, it even controls the metabolic rates in people, and controls our own bodies heat. Calorimetry can take place in any closed container which does not exchange heat with the surrounding environment. Any such container which is closed off from the environment is called a calorimeter.

1. 1. Introduction
2. 2. Outside Links
3. 3. References
4. 4. Contributors

Introduction

To calculate the amount of heat released or absorbed by a reaction with calorimetry, the heat of reaction formula is used. For example, if 150 grams of lead at 100°C were placed in a calorimeter with 50 grams of water at 28.8°C and the resulting temperature of the mixture was 22°C. We know that the specific heat of water is 4.184 J/g °C and the specific heat of lead is 0.128 J/g °C. Using calorimetry we can calculate the amount of heat gained and lost by each part of the system, so in this example we could calculate the amount of heat lost/gained by the water, the lead and the calorimeter. The amount of heat lost/gained by any part of the reaction is only related to the grams of the compound, its specific heat and the change in temperature it goes through, so we can relate each of the three parts together in the formula below.

The formula is Q = C x T where: Q = the amount of heat gained or lost C = the specific heat × mass and T = The final temperature of the mixture – the initial temperature of the substance

The heats of the different parts of the system can always be added up to equal zero because the amount of heat gained by one substance is equal to the amount lost by another. In the lead and water example the relationship would be as follows:

Q_lead+ Q_water +Q_calorimeter = 0

This can be helpful for calculating the heats of specific substances because any specific part of the equation can be subtracted to the other side of the equation and will equal the negative sum of the other two. If the heat of the water and the lead is known then the equation could be rearrange as such to find the heat of the calorimeter.

-(Q_lead) = Q_calorimeter.

With these two formulas we can now find the heats for all three parts of the reaction of lead and water using the information we started out with. For lead we know that:

Mass = 150 g, the initial temperature (T_i) = 100°C, and the specific heat (Csp) = 0.128 J/g °C

For water, mass = 50 g, T_i= 22°C, and C_sp = 4.184 J/g °C

And for the mixture of the two the final temperature (T_f) = 28.8°C

So with the two equations relating to heat we can calculate the amount of heat lost/gained for each separate part of the mixture

To calculate the amount of heat lost/gained by the lead we can use the firs equation, Q = C x T, because we have all the information needed to do. Q is the unknown, C = 0.128 J/g °C x 150g (specific heat x mass), and T = 28.8?C - 100°C (T_f – T_i) so the final calculation would go:

Qlead = 0.128 J/g °C x 150g x (28.8°C - 100°C) = -1.37 x 103 J

It is important to see that the heat for lead is negative because the lead declined in temperature and lost heat when it was mixed with water. The water temperature did the opposite when the lead was added to it and rose which tells us that the water gained heat when it was mixed with the lead and because we have the same information to start with we can use the same information to calculate exactly how much heat was gained, so

QH20 = 4.184 J/g °C x 50g x (28.8°C - 22°C) = 1.42 x 103 J

Now that we have the amount of heat which the lead lost and the amount that the water gained, we can find how much heat the calorimeter lost/gained by using the relationship -(Qlead + Qwater) = Qcalorimeter., so

Q_cal = -(Q_lead + Q_H20) = -(1.42 x 103 +-1.37 x103) = -50.0 J

With those calculations we now know that when the water and lead were mixed inside the calorimeter, the lead lost -1.37 x 103 J of heat, the water gained 1.42 x 103 J of heat, and the calorimeter lost -50.0 J of heat.

Calorimetry is a technique to measure the amount of heat energy created or absorbed in a chemical process. An attempt is made to conserve all the evolved heat using a calorimeter, a device containing a suitable liquid that makes good thermal contact with the process under investigation. 

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1. 1. Introduction
2. 2. Bomb and Coffee-Cup Calorimeters  
3. 3. References
4. 4. Outside Links
5. 5. Problems
6. 6.  

Introduction

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A calorimeter is a device used to measure the quantity of heat flow in a chemical reaction. Two of the most common types of calorimeters are the coffee cup calorimeter and the bomb calorimeter.

Bomb and Coffee-Cup Calorimeters  

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Coffee Cup Calorimeter
Coffee cup calorimeters are often utilized to demonstrate the concepts behind calorimetry. A known quantity of water is added into a polystyrene cup and a thermometer is inserted into the system so that the bulb is immersed in water. When a reaction occurs in this coffee cup calorimeter, the heat of the reaction will cause the water temperature to change.
This change  in water temperature is indicative of the amount of heat absorbed
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References

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Important Terms in Calorimeter

 

•Specific heat capacity, c

–Specific heat capacity, c of a substance is the amount of heat required to raise the temperature of one gram of the substance by one degree Celsius (Jg -1°C-1).

•Heat capacity, C

–Heat capacity,C is the amount of heat required to raise the temperature of a given quantity of the substance by one degree Celsius (J°C-1)