Thermochemistry: Viva Questions With Answers

Thermochemistry is one of the fields of chemistry that deals with energy changes. Enthalpy change of a reaction is defined as the difference in enthalpy of product and reactant. The heat evolved in a reaction does not transfer to the surrounding. It either increases or decreases the temperature of the system. The reaction is carried out in a calorimeter to determine the enthalpy change of a reaction. 

Table of Content

• Aim

• Apparatus Required

• Theory

• Procedure

• Observation

• Result

• Precautions

• Lab Manual Questions

• Viva Questions

• Practical Based Questions

• Conclusion

Aim

To determine the heat of neutralisation of a reaction between a strong acid and a strong base.

Apparatus Required

Following is the apparatus required for conducting the above experiment

• Beakers

• 0.2M HCL (100ml)

• 0.2M NaOH (100ml)

• Distill water

Theory

The heat of neutralisation is defined as the change in enthalpy when 1 gram equivalent of an acid is mixed with 1 gram equivalent of a base in an aqueous solution. The enthalpy of neutralisation for strong acid and strong base is 57.1kj/mol.

H++OH- = H2O, ∆H= -57.1kj/mol.

The enthalpy of neutralisation may be positive or negative. 

Procedure

The following steps must be followed while performing the procedure.

• Take 100 ml of  0.2M hydrochloric acid in a beaker and keep it in a thermally insulated wooden box. Remember to find its water equivalent and note its temperature.

• Now take another beaker and fill it with 100 ml of 0.2M sodium hydroxide. Note down its temperature also. Both solutions, hydrochloric acid and sodium hydroxide, should have the same temperature. If they do not have the same temperature, wait to attain the same temperature. 

• Now add sodium hydroxide in the beaker containing hydrochloric acid 

• Stir the mixture and note down the temperature of the mixture. 

Observations

The volume of hydrochloric acid = volume of sodium hydroxide = 100 ml = 100gm

The temperature of hydrochloric acid = temperature of sodium hydroxide = t4°C.

The temperature of hydrochloric acid + temperature of sodium hydroxide = t5°C.

Results

The enthalpy of neutralisation for a strong acid and strong base is 57.1KJ/mol. 

Precautions

Certain precautions must be followed while experimenting. These precautions are mentioned below:

• The temperature of the acid and base should be the same

• All the temperatures should be noted carefully

• Insulate the beaker 

Lab Manual Questions

Q1 Define enthalpy of neutralisation.

Ans: It is defined as the change in enthalpy on mixing 1 gram equivalent of acid with 1 gram of base.

Q2 Define enthalpy of reaction.

Ans: It is the difference in the product's and reactant's heat at constant temperature and pressure.

Q3 What is heat capacity?

Ans: Heat capacity is required to raise the temperature by 1°C.

Viva Questions

Q1 What is the significance of thermochemistry?

Ans: Thermochemistry is a critical field because it helps us to know whether a particular reaction will occur or not; it also helps us to know whether the reaction is endothermic or exothermic.

Q2 What do you mean by the enthalpy of the solution?

Ans: Enthalpy change on dissolving 1 mole of a substance above solvent at constant temperature and pressure. 

Q3 Define one calorie.

Ans: One calorie is the heat required to raise the temperature of 1 gram of water by 1°C.

Q4 Define Hess law.

Ans:  Hess law is defined as the energy changes in the overall reaction as the sum of energy changes of individual reactions.

Q5 What are the applications of Hess law?

Ans: It is used to calculate heat change of phase transition and also used to calculate the lattice energy of ionic compounds.

Q6 How do you calculate delta h for process ch3cooh?

Ans: delta h for the process ch3cooh is calculated by the following method. By combusting acetic acid with oxygen, we got the energy of carbon dioxide and water, after subtracting the product's energy from the reactant.

Q7 How will you define the path function?

Ans: Path functions are those of thermochemistry that depends on the path of a reaction. These are working, heat.

Q8 Is temperature a path function?

Ans: Temperature is not a path function but a state function.

Practical Based Questions

Q1 Total energy of a system is 

1. P.E + K.E

2. K.E+ heat energy

3. Both of the above

4. None of the above

Ans: P.E+K.E

Q2 Thing which depends on the initial and final state of a system is 

1. State function

2. Path function

3. Both of the above

4. None of the above

Ans: 1. State function

Q3 Which of the following is not a state function

1. Internal energy

2. Gibbs energy

3. Enthalpy

4. Work

Ans: 4. Work

Q4 If the internal energy of the system is increased

1. A chemical reaction may take place

2. The temperature of the system may rise

3. Change in the state te of the system is increased

4. All of the above

Ans: 4. All of the above

Q5 Which of the following is correct for the spontaneous endothermic process?

1. H<0

2. G<0

3. S<0

4. G>0

Ans: 2. G<0

Q6 A reaction has H and S both positive. The reaction will be

1. Spontaneous

2. Spontaneous and temperature dependent

3. Has an increasing free energy

4. Nonspontaneous

Ans: 4. Nonspontaneous

Q7 The environment in which a system is studied

1. State function

2. Phase

3. Surrounding

4. State

Ans: 3. Surrounding

Q8 Heat of neutralisation is minimum for which reaction?

1. Sodium hydroxide + sulphuric acid

2. Ammonium hydroxide + acetic acid

3. Sodium hydroxide + hydrochloric acid

4. Sodium hydroxide + acetic acid

Ans: 2. Ammonium hydroxide + acetic acid

Conclusion

• In this article, we studied thermochemistry and learned how to determine the heat of neutralising a strong acid and a strong base.

• We have also learned that the enthalpy of neutralisation for a strong acid and strong base is highest at 57.1 KJ/mol.

• For weak acids and weak bases, the enthalpy of neutralisation is always less than 57.1 KJ/mol.