Thermodynamics Test

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Thermodynamics Test - 44

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Weekly Quiz Competition

Question 1
1 / -0

Calculate work done.

A
$$12$$ atm $$\times$$ lt

B
$$24$$ atm $$\times$$ lt

C
$$48$$ atm $$\times$$ lt

D
$$36$$ atm/l

Solution

$$w=$$ area under curve $$=(12-4)(5-2)=24$$ atm $$\times$$ lt.
Question 2
1 / -0

In which process volume increases?

A
AB, CD

B
AB, BC

C
CD, DA

D
BC, CD

Solution

In Process AB, T is constant by entropy increases thus increasing volume, in BC, T decreasing with entropy is small that also increases volume.
Question 3
1 / -0

Hess' Law and bond energy data can be used to calculate the enthalpy change of a reaction. Bromoethane, $$CH_2CH_2Br$$, can be made by reacting ethene with hydrogen bromide.
$$CH_2=CH_2+HBr\rightarrow CH_3CH_2Br$$
What is the enthalpy change for this reaction?

A
$$-674$$ kJ $$mol^{-1}$$

B
$$-64$$ kJ $$mol^{-1}$$

C
$$+186$$ kJ $$mol^{-1}$$

D
$$+346$$ kJ $$mol^{-1}$$

Solution

$$\text{The enthalpy change is the difference of the enthalpy of product to the reactans.}$$
$$\text{By putting the values we get option B is the correct option.}$$
Question 4
1 / -0

The resultant heat change in a reaction is the same whether it takes
place in one or several stages. This statement is called:

A
Lavoisier and Laplace law

B
Hess's law

C
Joule's law

D
Le-chatelier's principle

Solution

The enthalpy change for the overall process is the sum of the enthalpy change of the steps in the process.
Question 5
1 / -0

An ideal gas undergoes a cyclic process as shown in figure;
$$\Delta u_{BC}=-5 KJ mol^{-1}, q_{AB}= 2 KJ mol^{-1}$$
$$w_{AB}= -5 KJ mol^{-1},W_{CA}=3 KJ mol^{-1}$$
Heat absorbed by the system during process $$CA$$ is

A
$$-5 KJ mol^{-1}$$

B
$$+5 KJ mol^{-1}$$

C
$$-18 KJ mol^{-1}$$

D
$$+18 KJ mol^{-1}$$

Solution
Question 6
1 / -0

For which of the following reaction $$\Delta H$$ is equal to $$\Delta u$$?

A
$$ 2HI(g) \leftrightharpoons H_2(g)+I_2(g)$$

B
$$ 2NO_2(g) \leftrightharpoons N_2O_4(g)$$

C
$$N_2(g) + 3H_2(g) \leftrightharpoons 2 NH_3(g)$$

D
$$ 2SO_2(g) +O_2(g) \leftrightharpoons 2SO_3(g)$$

Solution

B.$$\Delta n =-1$$
C. $$\Delta n=-2$$
D. $$\Delta n=-1$$
Option A is correct.
Question 7
1 / -0

Which statement about reactions that produce heat is not correct?

A
Burning magnesium produces hear energy

B
The overall reaction is exothermic

C
The products have more energy than the reactants

D
The temperature of the surroundings increases

Solution

$$\text{In a exothermic reaction heat is released for stability of product with less energy.}$$
Question 8
1 / -0

In which case is a reaction possible at any temperature?

A
$$\Delta H < 0, \Delta S > 0$$

B
$$\Delta H < 0, \Delta S > 0$$

C
$$\Delta H < 0, \Delta S > 0$$

D
None of these

Solution

$$\Delta G=-ve$$ if $$\Delta H =-ve$$ and $$\Delta S=+ve$$.

At any temp, because of t(K)>0 always.

Hence, option A is correct.
Question 9
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A gas is expanded from volume $$ V_0$$ and $$2V_0 $$ under three different processes. Process 1 is isobaric, process 2 is isothermal and process 3 is adiabatic . Let $$ \triangle U_1, \triangle U_2 $$ and $$\triangle U_3 $$ be the change in internal energy of the gas in these process. then :

A
$$ \triangle U_1 > \triangle U_2 > \triangle U_3 $$

B
$$ \triangle U_1 < \triangle U_2 < \triangle U_3 $$

C
$$ \triangle U_2 < \triangle U_1 < \triangle U_3 $$

D
$$ \triangle U_2 < \triangle U_3 < \triangle U_1 $$

Solution

Since $$U_1$$ is increasing in the graph than $$U_2$$ where slope is decreasing and then $$U_3$$ slope is more negative than $$U_2$$.
Question 10
1 / -0

In a reaction $$\Delta H$$ and $$\Delta S$$ both are more than zero. In which of the following cases would the reaction be spontaneous?

A
$$\Delta H > T\Delta S$$

B
$$T\Delta S > \Delta H$$

C
$$\Delta H = T\Delta S$$

D
None of these

Solution

A reaction will be spontaneous if:

$$\Delta G<O$$

$$\Delta H-T\Delta S < 0$$

$$\rightarrow \Delta H <T\Delta S$$