Worksheet on Enthalpies of reaction

Enthalpies of reaction is also called as energy change of a reaction.It is the amount of heat absorbed in reaction. Enthalpy of reaction depends on the state of reactants and products.

Here you can find questions related to ” Enthalpies of Reaction” and their answers:


1. Heat of transition is the heat evolved or absorbed when a substance is converted from:

(a)    One allotropic form to another allotropic

(b)   Liquid to vapour

(c)    Solid to vapour

(d)   Solid to liquid


2. The heat absorbed in a reaction at constant temperature and volume is equal to:

(a)    \Delta U of the reaction

(b)   \Delta H of the reaction

(c)    \Delta U of the reaction

(d)   -\Delta H of the reaction


3. Which of the following statements is correct about heat of combustion?

(a)    It may be exothermic in some cases and endothermic in other cases

(b)   It is always an exothermic reaction

(c)    It is applicable to gaseous substances only

(d)   Its value does not change with temperature.


4. The amount of heat measured for a reaction in a bomb calorimeter is:

(a)    \Delta G

(b)   \Delta H

(c)    P \Delta V

(d)   \Delta E


5. The calorific value of fat is:

(a)    Less than that of carbohydrates and protein

(b)   Less than that of protein but more than carbohydrates

(c)    Less than that of carbohydrates but more than that of protein

(d)   More than that of carbohydrate and protein


6. Heat exchanged in a chemical reaction at constant temperature and pressure is called:

(a)    Free energy

(b)   Internal energy

(c)    Enthalpy

(d)   Entropy


7.  The enthalpy change for a reaction does not depend upon:

(a)    Use of different reactants for the same products

(b)   The nature of intermediate reaction steps

(c)    The difference in the initial and final temperature of involved substances

(d)   The physical state of reactants and products


8. The amount of energy released when 20 ml of 0.5 M NaOH is mixed with 100 ml of 0.1 M HCI is x kJ. The heat of neutralization (in kJ mol^{-1}) is:

(a)    +100x

(b)   –100x

(c)    +50x

(d)   -50x


9. The heat of combustion of yellow P and red P is -9.91 kJ and -8.78 kJ respectively. The heat of transition of yellow P red P is:

(a)    +18.69 kJ

(b)   +1.13 kJ

(c)    -18.69 kJ

(d)   -1.13 kj


10. The heat of neutralization of a strong acid and a strong alkali is 57.0 kJ mol^{-1}. The heat released when 0.5 mole of HNO_3 solution is mixed with 0.2 mole of KOH is:

(a)    57.0 kJ

(b)   11.4 kJ

(c)    29.5 kJ

(d)   34.6 kJ


11. The heat of combustion of CH_4(g), C (graphite), H_2 (g) is -20 kcal, 40 kcal, -10 kcal, respectively. The heat of formation of methane is:

(a)    -40 kcal

(b)   +50 kcal

(c)    -80.0 kcal

(d)   +80 kcal


1.(a)     2. (a)     3. (b)     4. (d)     5. (d)     6. (c)     7. (b)     8. (b)     9. (d)     10. (b)     11. (a)

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