Previous Year Papers

Download Solved Question Papers Free for Offline Practice and view Solutions Online.

Test Series

Take Zigya Full and Sectional Test Series. Time it out for real assessment and get your results instantly.

Test Yourself

Practice and master your preparation for a specific topic or chapter. Check you scores at the end of the test.

Thermodynamics

Long Answer Type

181.

Explain the origin of enthalpy change in a direction. interest

132 Views

182. What do you mean by enthalpy (heat) of reaction? Name the factors that influence the enthalpy of reaction.

99 Views

Short Answer Type

183.

What is standard enthalpy change (∆_rH⁰) of a reaction?

155 Views

184. What do you mean by enthalpy (heat) of combustion? Give three examples.

97 Views

185.

What do you mean by the standard enthalpy of combustion?

109 Views

186. Combustion of glucose is according to the following reaction:

straight C subscript 6 straight H subscript 12 straight O subscript 6 left parenthesis straight s right parenthesis space plus space 6 straight O subscript 2 left parenthesis straight g right parenthesis space rightwards arrow space space 6 CO subscript 2 left parenthesis straight g right parenthesis space plus space 6 straight H subscript 2 straight O left parenthesis straight g right parenthesis semicolon space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space increment straight H space equals space minus 250 space kJ

How much heat energy is needed for the formation of 1.8g of glucose?

111 Views

187. Enthalpy of combustion of carbon to CO₂ is –393.5 kJ mol^–1. Calculate the heat released upon formation of 35.2 g of CO₂ from carbon and dioxygen gas.

228 Views

188.

What will be the amount of heat evolved when 39 gm of C₆H₆(l) are burnt? Given that:
$straight C subscript 6 straight H subscript 6 left parenthesis straight l right parenthesis space plus space 15 over 2 straight O subscript 2 left parenthesis straight g right parenthesis space space rightwards arrow space space 3 straight H subscript 2 straight O left parenthesis straight l right parenthesis space plus space 6 CO subscript 2 left parenthesis straight g right parenthesis semicolon increment straight H space equals space minus 3264.6 space kJ space mol to the power of negative 1 end exponent$

93 Views

189.

How much heat is evolved when 204g of ammonia are produced according to the equation,

$space straight N subscript 2 left parenthesis straight g right parenthesis space plus space 3 straight H subscript 2 left parenthesis straight g right parenthesis space rightwards arrow space space 2 NH subscript 3 left parenthesis straight g right parenthesis semicolon space increment straight H space equals space 92.6 space kJ$

106 Views

Long Answer Type

190.
Explain:
(i) Enthalpy (heat) of the formation.

(ii) Standard enthalpy of formation. How is it helpful in calculating the enthalpy of a reaction?

Enthalpy of formation: It is the enthalpy (heat) change accompanying the formation of one mole of a compound from its elements. It is denoted by ∆H_fe.g.

Hence enthalpy of formation of water i.e. ∆H_f(H₂O) = –285.9 kJ

Standard enthalpy of formation: When all the species of the chemical reaction are in their standard states, the enthalpy of formation is called standard enthalpy of formation. It is denoted by ∆_fH°. Standard enthalpy of formation of a compound is defined as the enthalpy change accompanying the formation of one mole of a compound from its constituent elements, all the substances being in their standard states (1 bar pressure and 298 K). For example

It should be noted that standard enthalpies of elementary substances are taken to be zero.
Calculation of enthalpy of reaction (∆H): By knowing the standard enthalpies of formation of various substances, we can calculate the standard enthalpy change of any reaction.

Standard enthalpy change of reaction = [Standard enthalpies of formation of all products]
- [Standard enthalpies of formation of all reactants]

i.e.