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The enthalpy change (∆H) for the reaction
$straight N subscript 2 left parenthesis straight g right parenthesis space plus space 3 straight H subscript 2 left parenthesis straight g right parenthesis space space rightwards arrow space space 2 NH subscript 3 left parenthesis straight g right parenthesis$
is -92.38 kJ at 298 K. what is the $increment straight U$ at 298 K?

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162.

∆U^⊝ of combustion of methane is –X kJ mol^–1. The value of ∆H^⊝ is :

(i) = ∆U^⊝

(ii) > ∆U^⊝

(iii) < ∆U^⊝

(iv) = 0

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Long Answer Type

163. The reaction of cyanamide, NH₂CN (s), with dioxygen was carried out in a bomb calorimeter, and ∆U was found to be –742.7 kJ mol^–1 at 298 K. Calculate enthalpy change for the reaction at 298 K.

NH subscript 2 CN left parenthesis straight g right parenthesis space plus space 3 over 2 straight O subscript 2 left parenthesis straight g right parenthesis space space rightwards arrow space space space space straight N subscript 2 left parenthesis straight g right parenthesis space plus space CO subscript 2 left parenthesis straight g right parenthesis space plus space straight H subscript 2 straight O left parenthesis straight l right parenthesis

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164. The heat of combustion of C₆H₅COOH (benzoic acid) at constant volume is measured in a bomb calorimeter at 300K and is found to be – 3199.76kJ mol^–1. Find the value of enthalpy change. (R = 8.31 JK^–1 mol^–1).

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Short Answer Type

165.

What do you understand by:
(i) Heat capacity of a substance
(ii) Heat capacity at constant volume
(iii) Heat capacity at constant pressure?

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166. Suppose a piece of metal requires 6.80J of heat to raise the temperature by one degree Celsius at constant volume. Calculate the quantity of heat required to raise the temperature of a piece of metal from 20.0°C to 30.0°C.

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167.

What do you understand by: (i) Specific heat capacity (ii) Molar heat capacity?

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168.
60.8 J of energy is required to change the temperature of 25.0 g of ethylene glycol (a compound used as an antifreeze in automobile engines) by 1.0 K. Calculate heat capacity of ethylene glycol.

We know that



Here, q = 68.8J; m = 25.0 g,

Substituting the values in eq. (1), we have,

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169. Calculate the number of kJ of heat necessary to raise the temperature of 60.0g of aluminium from 35 to 55°C. Molar heat capacity of aluminium is 24 J mol^–1 K^–1.

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170. Calculate the energy needed to raise the temperature of 10.0 g of iron from 25°C to 500°C if specific heat capacity of iron is 0.45 J(°C)^–1 g^–1.

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