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Class first year MCQs on Thermochemistry

1.Which of the following substances have zero value for their standard enthalpy of formation?





... Answer is d)
Explanation: The standard enthalpy of formation of a substance is defined as enthalpy change when one of the substance is formed at standard conditions (1atm, and 273 K) from its element at the same standard conditions. For pure elements, that naturally exist at standard states, enthalpy of formation is taken arbitrarily zero.

2. Calorie is equivalent to .





... Answer is a)
Explanation: 1 cal. is equal to 4.18 joule.

3. Enthalpy of neutralization of all the strong acids and strong bases have the same value due to ?





... Answer is c)
Explanation: Enthalpy of neutralization of all the strong acids and strong bases have the same value. This is because strong acids and bases completely ionize and produce the same number of H+ and OH-

4. Total heat content of a system is called





... Answer is a)
Explanation: By definition, enthalpy is sum of total internal energy (E) and product of pressure-volume (PV) work.
Mathmatically,
H = E + PV
As this relation shows the complete heat content of the system, so it is also called as total heat content of the system.

5. Heat of -------of a substance is always negative





... Answer is b)
Explanation: Combustion is a chemical reaction between a fuel (such hydrocarbons) and an oxidant (such as oxygen). This reaction always produces heat (exothermic) along with formation of water and carbon dioxide.

6. A balloon filled with oxygen is placed in a freezer. Identify the system





... Answer is b)
Explanation: Anything that is under study is called system. In above example, a balloon filled with oxygen is placed in freezer in oder to determine of effect of temperature on volume of gas. Therefore oxygen is the system.

7. A bomb calorimeter is used in --------calorimetery





... Answer is a)
Explanation: A bomb calorimeter is used to determine the heat available in food. As bomb calorimeter is a closed container, so it is constant volume colorimeter.

8. Born Haber cycle is used to determine lattice energies of





... Answer is b)
Explanation: lattice energy is the amount of energy released when one mole of a solid compound is formed from its gasous ions. Lattic energy cannot be determined directly by colorimetr, therefore, Born Haber cycle is used to determine the lattic energy.

9. q = ∆H When





... Answer is d)
Explanation: q = ∆H when pressure is kept constant (i.e. ∆P = 0)

10. Enthalpy of combustion for C is -393.5 kJ/mole

Enthalpy of formation of +O2 would be When





... Answer is b)
Explanation: Combustion of C is the reaction between carbon and oxygen to produce the CO2 and water alongwith heat energy. Formation of CO2 also involves the same reaction. So, enthalpy change in both reactions is same i.e., -393.5 kJ.

11. Which of the following is not a state function of a system?





... Answer is d)
Explanation:

12. For writing a thermochemical equation for enthalpy of combustion of an element requirs:

(a) 1 mole of element as reactant
(b) 1 mole of oxide of element as product
(c) Standard states of all the substances
(d) Balanced equation of 1 mole of element




... Answer is c)
Explanation:
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