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CBSE - Class 11 Chemistry Thermodynamics Worksheet

1.
For an isolated system, $ΔU = 0$, what will be $ΔS$ ?
2.
Choose the correct answer. A thermodynamic state function is a quantity
a. used to determine heat changes b. whose value is independent of path c. used to determine pressure volume work d. whose value depends on temperature only.
3.
Calculate the enthalpy change for the process
$CCl_4(g) \rightarrow C(g) + 4 Cl(g)$
and calculate bond enthalpy of C – Cl in $CCl_4(g)$.
$Δ_{vap}H^o(CCl_4) = 30.5 \text{ kJ mol}^{-1}$.
$Δ_fH^o (CCl_4) = -135.5 \text{ kJ mol}^{-1}$.
$Δ_aH^o (C) = 715.0 \text{ kJ mol}^{-1}$, where $Δ_aH^o$ is enthalpy of atomisation
$Δ_aH^o (Cl_2) = 242 \text{ kJ mol}^{-1}$
4.
The reaction of cyanamide, $NH_2CN (s)$, with dioxygen was carried out in a bomb calorimeter, and $ΔU$ was found to be $-742.7 \text{ kJ mol}^{-1}$ at 298 K. Calculate enthalpy change for the reaction at 298 K.
$NH_2CN(g) + \frac{3}{2}O_2(g) \rightarrow N_2(g) + CO_2(g) + H_2O(l)$
5.
Calculate the standard enthalpy of formation of $CH_3OH(l)$ from the following data:
$CH_3OH (l) + \frac{3}{2} O_2(g) \rightarrow CO_2(g) + 2H_2O(l)$ ; $Δ_rH^o = -726 \text{ kJ mol}^{-1}$
$C(graphite) + O_2(g) \rightarrow CO_2(g)$ ; $Δ_cH^o = -393 \text{ kJ mol}^{-1}$
$H_2(g) + \frac{1}{2} O_2(g) \rightarrow H_2O(l)$; $Δ_fH^o = -286 \text{ kJ mol}^{-1}$.
6.
Given
$N_2(g) + 3H_2(g) \rightarrow 2NH_3(g)$; $Δ_rH^o = -92.4 \text{ kJ mol}^{-1}$
What is the standard enthalpy of formation of $NH_3$ gas?
7.
$ΔU^o$ of combustion of methane is $-X \text{ kJ mol}^{-1}$. The value of $ΔH^o$ is
a. $= ?U^o$ b. > $?U^o$ c. < $?U^o$ d. $= 0$
8.
The equilibrium constant for a reaction is 10. What will be the value of $ΔG^o$ ? $R = 8.314 \text{ JK}^{-1} \text{ mol}^{-1}$, $T = 300 K$.
9.
The enthalpies of all elements in their standard states are:
a. unity b. zero c. < 0 d. different for each element
10.
For the reaction
$2 A(g) + B(g) \rightarrow 2D(g)$
$ΔU^o = -10.5 \text{ kJ}$ and $ΔS^o = -44.1 \text{ JK}^{-1}$.
Calculate $ΔG^o$ for the reaction, and predict whether the reaction may occur spontaneously.
11.
For the reaction,
$2 Cl(g) \rightarrow Cl_2(g)$, what are the signs of $ΔH$ and $ΔS$ ?
12.
For the reaction at 298 K,
$2A + B \rightarrow C$
$ΔH = 400 \text{ kJ mol}^{-1}$ and $ΔS = 0.2 \text{ kJ K}^{-1} \text{ mol}^{-1}$
At what temperature will the reaction become spontaneous considering $ΔH$ and $ΔS$ to be constant over the temperature range.
13.
Enthalpy of combustion of carbon to $CO_2$ is $-393.5 \text{ kJ mol}^{-1}$. Calculate the heat released upon formation of 35.2 g of $CO_2$ from carbon and dioxygen gas.
14.
Calculate the enthalpy change on freezing of 1.0 mol of water at $10.0^\circ C$ to ice at $-10.0^\circ C$. $Δ_{fus}H = 6.03 \text{ kJ mol}^{-1}$ at $0^\circ C$.
$C_p [H_2O(l)] = 75.3 \text{ J mol}^{-1} K^{-1}$
$C_p [H_2O(s)] = 36.8 \text{ J mol}^{-1} K^{-1}$
15.
Calculate the number of kJ of heat necessary to raise the temperature of 60.0 g of aluminium from $35^\circ C$ to $55^\circ C$. Molar heat capacity of Al is $24 \text{ J mol}^{-1} K^{-1}$.
16.
In a process, 701 J of heat is absorbed by a system and 394 J of work is done by the system. What is the change in internal energy for the process?
17.
A reaction, $A + B \rightarrow C + D + q$ is found to have a positive entropy change. The reaction will be
a. possible at high temperature b. possible only at low temperature c. not possible at any temperature d. possible at any temperature
18.
Calculate the entropy change in surroundings when 1.00 mol of $H_2O(l)$ is formed under standard conditions. $Δ_fH^o = -286 \text{ kJ mol}^{-1}$.
19.
The enthalpy of combustion of methane, graphite and dihydrogen at 298 K are, $-890.3 \text{ kJ mol}^{-1}$, $-393.5 \text{ kJ mol}^{-1}$, and $-285.8 \text{ kJ mol}^{-1}$ respectively. Enthalpy of formation of $CH_4(g)$ will be
a. $-74.8 \text{ kJ mol}^{-1}$ b. $-52.27 \text{ kJ mol}^{-1}$ c. $+74.8 \text{ kJ mol}^{-1}$ d. $+52.26 \text{ kJ mol}^{-1}$
20.
Comment on the thermodynamic stability of $NO(g)$, given
$\frac{1}{2} N_2(g) + \frac{1}{2}O_2(g) \rightarrow NO(g)$; $Δ_rH^o = 90 \text{ kJ mol}^{-1}$
$NO(g) + \frac{1}{2}O_2(g) \rightarrow NO_2(g)$: $Δ_rH^o= -74 \text{ kJ mol}^{-1}$

Worksheet Answers

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