Thermochemistry

Introduction

Is the heat gain by a cold body always equal to heat loss by a hot body? Yes, it is true. Heat gain by a cold body always equals heat loss by a hot body. It is the principle of the calorimeter. There is no energy loss. Energy is always conserved; it can only be converted from one form to another. Do you know what heat capacity is and how it can be calculated?

To know more about calorimeters and water equivalents, continue reading this article! 

Table of Content

• Aim

• Apparatus Required

• Theory

• Procedure

• Observations

• Results

• Precautions

• Lab Manual 

• Viva Questions

• Practical Based Questions

Aim

To determine the water equivalent of a calorimeter. 

Apparatus Required

• Calorimeter

• Thermometer

• Distilled water

• 250ml Beaker

• Cotton

• Hot plate

• Measuring jar

• Wooden box with lid

• Stirrer

Theory

The water equivalent of a calorimeter is defined as the amount (mass) of water that will absorb or lose the same quantity of heat as any other given substance for the exact change in temperature. It is necessary to measure the water equivalent for correct calculation. Because during the heat exchange calorimeter also takes or loses some heat or energy. There are different types of calorimeters - adiabatic calorimeter, reaction calorimeter, constant pressure calorimeter, and differential scanning calorimeter. 

Procedure

• Take 50 ml of water in a calorimeter using a measuring jar

• Then measure the temperature of the water using a thermometer in a calorimeter. Let's assume the temperature of the water is t1°C.

• The calorimeter is placed in a wooden box, and cotton is filled in the space between the calorimeter to avoid heat loss. 

• Now a stirrer is inserted into the calorimeter.

• Pour 50 ml of distilled water is in the beaker, then  heat the water  

• Stop heating, and note the temperature of the water. Lets the temperature of the water be t2 

• Add warm water to the calorimeter

• Now stir the water and note the reading

• Continue stirring water using a stirrer until its temperature becomes constant. Let the temperature be t3. 

Observations

• The volume of water in the calorimeter is 50 ml

• The temperature of the water is t1

• The volume of water added is 50ml

• The mass of water is 50g

• The temperature of warm water is t2

• Temperature after mixing is t3

By using the formula 

Heat given by hot water = heat taken by cold water

We can calculate the water equivalent of a calorimeter by the above formula. 

Results

The water equivalent of the calorimeter can be calculated by the above formula. 

Precautions

Several precautions need to be followed while experimenting. These precautions are mentioned below.

1. The final temperature should be noted only after stirring the solution well.

2. All the temperatures should be noted carefully.

3. Insulate the beaker thermally as perfectly as possible. 

Lab Manual Questions 

Q1 What do you mean by water equivalent?

Ans: Water equivalent is the amount of heat required to increase the temperature of any substance by one degree. 

Q2 What is the principle of finding the water equivalent?

Ans: Heat gain is equal to the heat loss principle used to find the water equivalent of the calorimeter.

Q3 Define the enthalpy of a reaction.

Ans: The enthalpy of a reaction is defined as the difference in the heat content of the reactant and product of a chemical reaction at constant pressure. 

Viva Questions

Q1 What is thermochemistry?

Ans: Thermochemistry is the study of energy changes in a chemical reaction.

Q2 What is an exothermic reaction

Ans: Exothermic reactions are those reactions that release heat or energy.

Q3 What do you mean by an enthalpy of the solution?

Ans: Enthalpy of a solution is the change in energy when a one-mole substance is dissolved in a solvent at constant temperature and pressure.

Q4 Define heat capacity?

Ans: Heat capacity is the heat required to raise the temperature by one-degree celsius.

Q5 What is the first law of thermodynamics?

Ans: The first law of thermodynamics defines energy that cannot be created or destroyed. It can be converted only from one form to another form.

Q6 What is the principle used for determining the heat of neutralisation?

Ans: Hea gain = Heat loss is the principle used for determining the heat of neutralization.

Q7 What is the principle of the calorimeter?

Ans: Heat gain by a cold body always equals heat loss by a hot body.

Q8 What are thermochemical equations?

Ans: Thermochemical equations are balanced chemical equations with their physical states. 

Practical Based Questions

Q1 What is the most expected error in determining the heat of neutralisation?

1. Temperature error

2. Systematic error

3. Both of the above

4. None of the above

Ans: 1. Temperature error

Q2 What is the value of enthalpy of neutralisation of strong acid and a strong base?

1. 62.4 kj/mol

2. 50 kj/mol

3. 57.1 kj/mol

4. None of the above

Ans: 57.1 kj/mol 

Q3 In endothermic reactions, heat is

1. Absorbed 

2. Released

3. Both of  the above

4. None of the above

Ans: 1. Absorbed

Q4 What type do deviation is observed in the acetone and chloroform mixture?

1. Positive deviation

2. Negative deviation

3. Both of the above

4. None of the above

Ans: 2. Negative deviation.

Q5 Heat evolved or absorbed on mixing chloroform and acetone

1. Evolve

2. Absorbe

3. Remain same

4. None of the above

Ans: 1. Evolve

Q6 In which of the following reactions will the product be stable?

1. Endothermic reactions

2. Exothermic reaction

3. Both of the above

4. None of the above

Ans: 1. Exothermic reaction

Q7 For which of the following substances is the heat of formation in the standard state 0?

1. Carbon dioxide

2. C (diamond)

3. Ozone

4. C (graphite)

Ans: 4. C (graphite)

Q8 If the change of enthalpy is negative, what will be the reaction?

1. Endothermic reactions

2. Exothermic reaction

3. Maybe exothermic or endothermic reactions

4. None of the above

Ans: 2. Exothermic reaction. 

Conclusion

• In this article, we have discussed calorimeter and its principle

• We have also discussed how to measure the water equivalent of a calorimeter.

• Calorimeter, thermometer, beaker, and distilled water are some of the articles required for this experiment. 

• Certain precautions, such as proper temperature measurement, must be followed while experimenting.