Seventh Chapter Solved Exercise MCQs Of FSc First Year Chemistry

by

Seventh chapter Thermochemistry solved Exercise MCQs with explanation

1: If an endothermic reaction is allowed to take place very rapidly in the air, the temperature of the surrounding air;

  1. Remains constant
  2. Increases
  3. Decreases
  4. Remains unchanged

Explanation:

In endothermic reaction, the heat is absorbed. This heat is taken by the system from surrounding, hence the temperature of surrounding air falls. So, option (c) is correct.

Also Read

First Chapter Solved Exercise MCQs Of FSc First Year Chemistry

Second Chapter Solved Exercise MCQs Of FSc First-Year Chemistry

Fifth Chapter Solved Exercise MCQs Of FSc First Year Chemistry

2: In endothermic reactions, the heat content of the;

  1. Products is more than the reactants
  2. Reactants is more than the products
  3. Both (a) and (b)
  4. Reactants and products are equal.

Explanation

When the reaction is endothermic, it absorbs the heat. It means that the heat content of products becomes bigger than those of reactants. So, option (a) is correct.

3: Calorie is equivalent to:

  1. 0.4184 J
  2. 41.84 J
  3. 4.184 J
  4. 418.4 J

Explanation

A calorie is bigger unit of energy than Joule .

1 calorie =4.184 j So, option (c) is correct.

4: The change in heat energy of a chemical reaction at constant temperature and pressure is called:

  1. Enthalpy change
  2. Bond energy
  3. Heat of sublimation
  4. Internal energy change

Explanation

Whenever a change of heat energy takes place at constant temperature and pressure, then it is called enthalpy change of reaction. So, option (a) is correct.

5: Which of the following statements is contrary to the first law of thermodynamics?

  1. Energy can neither be created nor be destroyed.
  2. One form of energy can be transferred into an equivalent amount of other kinds of energy.
  3. In an adiabatic process, the work done is independent of the path.
  4. Continuous production of mechanical work without supplying is possible

Explanation

According to the first law of thermodynamics, the amount of heat supplied is converted to an equivalent amount of work and if the quantity of work done is smaller than rest of the heat supplied is converted into internal energy of the system.

So, it is not possible to get continuous mechanical work without supplying an equivalent amount of heat. Hence, option (d) is correct.

6: For a given process, the heat changes at constant pressure (qp) and at constant volume (qv) are related to each other as:

  1. qp =qv
  2. qp ˂ qv
  3. qp ˃ qv
  4. d)qp =qv/2

Explanation

The amount of heat supplied to the system at constant pressure is always greater than amount of heat supplied at constant volume. When the process happens at constant pressure, then the expansion takes place and pressure volume work has to be done. Hence’

qp ˃ qv

So option (c) is correct.

7: For the reaction

NaOH + HCl   ↔   NaCl + H2O

The change in enthalpy is called:

  1. Heat of reaction
  2. Heat of sublimation
  3. Heat of neutralization
  4. Heat of combustion

Explanation

In the given reaction, a strong acid is reacted with strong base, they are neutralizing each other. The amount of heat evolved is called heat of neutralization. So, option (c) is correct.

8: The net heat change in a chemical reaction is same whatever it is brought about in two or more different ways in one or several steps. It is known as;

  1. Henry’s law
  2. Hess’s law
  3. Joule’s law
  4. Law of conservation of energy

Explanation:

It is just according to the Hess’s law of heat summation that the net heat change in a chemical reaction remains the same whether the reaction is brought about in two or more different ways or in several steps.

Hence, option (b) is correct.

9: Enthalpy of neutralization of all the strong acids and strong bases has the same value because;

  1. Neutralization leads to the formation of salt and water.
  2. Strong acids and bases are ionic substances.
  3. Acids always give rise to H+ ions and bases always furnish OH– ions to form water.
  4. The net chemical change involves the combination of H+ and OH– ions to form water.

Explanation:

In all the strong acids and bases, complete dissociations take place. So, H+ and OH– ions are present in the solution to the maximum extent.

The combination of these two ions to form water is an endothermic process and 13.6Kcal mol-1 of energy is evolved. This quantity is true for all strong acid sand bases.

So, option (d) is correct.