Thermodynamics Test

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Thermodynamics Test - 73

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Weekly Quiz Competition

Question 1
1 / -0

Heat of $$30 kcal$$ is supplied to a system and $$4200 J$$ of external work is done on the system so that its volume decreases at constant pressure. What is the change in its internal energy. $$=(J=4200J/kcal)$$

A
$$1.302\times 10^5J$$

B
$$2.302\times 10^5J$$

C
$$3.302\times 10^5J$$

D
$$4.302\times 10^5J$$

Solution

$$\Delta Q = 30 \times 4200$$
$$ = 126000J$$
$$\Delta W = - 4200J$$
$$\therefore \Delta u = \Delta Q - \Delta W$$
$$ = 126000 + 4200J$$
$$ = 1.302 \times {10^5}J$$
Hence,
option $$(A)$$ is correct answer.
Question 2
1 / -0

A diatomic gas is heated at constant at constant pressure. What fraction of the heat energy is used to increase the internal energy ?

A
$$\dfrac 3 5$$

B
$$\dfrac 3 7$$

C
$$\dfrac 5 7$$

D
$$\dfrac 5 9$$

Solution
Question 3
1 / -0

The $$\Delta H$$ and $$\Delta S$$ for a reaction at one atmospheric pressure are $$+30.558\ KJ$$ and $$+0.066\ KJ$$ respectively. The temperature at which the free energy changes will be zero and below this temperature, the nature of the reaction would be

A
$$483\ K,spontaneous$$

B
$$443\ K,non-spontaneous$$

C
$$463\ K,spontaneous$$

D
$$463\ K,non-spontaneous$$

Solution
Question 4
1 / -0

Given that:
(i) $$C$$ (graphite)$$+O_2(g)\rightarrow CO_2(g)$$; $$\quad \Delta _rH^o=x\ kJ mol^{-1}$$.
(ii) $$C$$ (graphite)$$+\dfrac{1}{2}O_2(g)\rightarrow CO(g)$$; $$\quad \Delta _rH^o=y\ kJ mol^{-1}$$
(iii) $$CO(g)+\dfrac{1}{2}O_2(g)\rightarrow CO_2(g)$$; $$\quad \Delta _rH^o=z\ kJ mol^{-1}$$

Based on the given thermochemical equations, find out which one of the following algebraic relationships is correct?

A
$$z=x+y$$

B
$$x=y-z$$

C
$$x=y+z$$

D
$$y=2z-x$$

Solution

$$C_{(graphite)}+O_2(g)\rightarrow CO_2(g)\Delta_rH^o=xkJ/mol$$ .$$(1)$$
$$C_{(graphite)}+\dfrac{1}{2}O_2(g)\rightarrow CO(g)\Delta_rH^o=ykJ/mol$$ ..$$(2)$$
$$CO(g)+\dfrac{1}{2}O_2(g)\rightarrow CO_2(g)\Delta_rH^o=zkJ/mol$$ .$$(3)$$
Now,
$$(1)=(2)+(3)$$
$$x=y+z$$.
Question 5
1 / -0

For $$1^{st}$$ law of thermodynamics, select the correct option.

A
The energy of a closed system is constant.

B
$$1^{st}$$ law is commonly started as the law of conservation of energy i.e energy can neither be created nor be destroyed

C
It is applicable only for reversible process.

D
Both (1) & (2)

Solution
Question 6
1 / -0

The internal energy of gases $$He, O_{2}$$ and $$NH_{3}$$ are plotted against the absolute temperature. The respective graphs $$1, 2$$ and $$3$$ are of?

A
$$He, O_{2}$$ and $$NH_{3}$$

B
$$NH_{3}, H_{2}$$ and $$O_{2}$$

C
$$NH_{3}, O_{2}$$ and $$He$$

D
$$O_{2}, He$$ and $$NH_{3}$$

Solution
Question 7
1 / -0

The sole criterion for the spontaneity of a process is

A
tendency to acquire minimum energy

B
Tendency to acquire maximum randomness

C
Tendency to acquire minimum energy and maximum randomness

D
tendency to acquire maximum stability
Question 8
1 / -0

Consider the following reaction
$${{\text{C}}_{\text{6}}}{{\text{H}}_{\text{6}}}\left( \ell \right){\text{ + }}\frac{{{\text{15}}}}{{\text{2}}}{{\text{O}}_{\text{2}}}\left( {\text{g}} \right) \to {\text{6C}}{{\text{O}}_{\text{2}}}\left( {\text{g}} \right){\text{ + 3}}{{\text{H}}_{\text{2}}}{\text{O}}(g)$$
Signs of $$\Delta {\text{H,}}\,\,\Delta {\text{S}}\,{\text{and}}\,\Delta {\text{G}}$$ for the above reaction will be:

A
+ , - , +

B
- , + , -

C
- , + , +

D
+ , + , -

Solution
Question 9
1 / -0

At $$ 27^oC $$ the reaction,
$$ C_6H_{6(1)} + \dfrac{15}{2} O_{2(g)} \rightarrow 6CO_{2(g)} +3H_2O_{(I)} $$
proceeds spontaneously because the magnitude of

A
$$ \Delta H=T\Delta S $$

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

C
$$ \Delta H\ <\ T\Delta S $$

D
$$ \Delta H\ >\ 0\ and\ T\Delta S\ <\ 0 $$

Solution
Question 10
1 / -0

A process has $$\Delta H = 200 \,J \,mol^{-1}$$ and $$\Delta S = 40 \,JK \,mol^{-1}$$. Out of the values given above which the process will be sponteneous:

A
$$5 \,K$$

B
$$4 \,K$$

C
$$20 \,K$$

D
$$12 \,K$$

Solution

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

$$T = \dfrac{\Delta H}{\Delta S} = \dfrac{200}{40} = 5K$$