Thermodynamics Test

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Thermodynamics Test - 40

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Weekly Quiz Competition

Question 1
1 / -0

$$C(s) + O_2(g) \to CO_2(g); \quad \Delta H = -94kcal$$

$$2CO(g) + O_2(g) \to 2CO_2(g); \quad \Delta H = -135.2 kcal$$

The heat of formation of $$CO(g)$$ is :

A
$$-26.4\ kcal$$

B
$$41.2\ kcal$$

C
$$26.4\ kcal$$

D
$$229.4\ kcal$$

Solution

Given,
$$C(s) + O_2(g) \to CO_2; \Delta H_1 = -94Kcal.$$ ....(1)

$$2CO(g) + O_2(g) \to 2CO_2(g); \Delta H_2= - 135.2 K \ cal.$$ ....(2)

$$\Delta H_f(CO)=?$$

Now the formation of $$CO$$ is

$$CO_2(g) + O_2(g) \to CO + \dfrac{1}{2}O_2(g)$$ ....(3)

Then, $$\Delta H_3 = \dfrac{135.2}{2} = 67.6K\ cal$$

$$\therefore $$ The required equation,

$$C(s) + \dfrac{1}{2} O_2= CO(g); \Delta H_4 = ?$$

Adding equation (1) and (3) we get

$$C(s) + \dfrac{1}{2} O_2 \to CO(g)$$;

$$\Rightarrow \Delta H = -94+67.6 = -26.4K cal$$.

$$\therefore$$ The heat of formation of $$CO(g)$$ is $$-26.4\ K\ cal$$.

Hence, te correct option is $$\text{A}$$
Question 2
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Suppose that a reaction has $$\Delta H=-40kJ$$ and $$\Delta S=-50J/K$$. At what temperature range will it change from spontaneous to non-spontaneous ?

A
$$0.79\ K$$ to $$0.81\ K$$

B
$$799\ K$$ to $$801\ K$$

C
$$801\ K$$ to $$799\ K$$

D
$$0.81\ K$$ to $$0.79\ K$$
Question 3
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Consider the reaction, $$2A_{(g)} + B_(g) rightleftarrow 2C_{(g)}$$ for which $$K_c = 350$$. If $$0.01$$ mole of each of the reactants and product are mixed in a $$2.0$$L flask, then the reaction quotient and the spontaneous direction of the system will be?

A
$$Q_c = 0.002$$; the equilibrium shifts to the left

B
$$Q_c = 2000$$; the equilibrium shifts to the left

C
$$Q_c = 0.002$$; the equilibrium shifts to the right

D
$$Q_c = 2000$$; the equilibrium shifts to the right

Solution
Question 4
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$$\Delta H$$ and $$\Delta S$$ are $$-283\ kJ$$ and $$-87\ J\ K^{-1}$$, respectively. It was intended to carry out this reaction at $$1000, 1500, 3000$$ and $$3500\ K$$. At which of these temperatures would this reaction be thermodynamically spontaneous?

A
$$1000, 1500$$ and $$2000\ K$$

B
$$500, 3000$$ and $$3500\ K$$

C
$$1500$$ and $$3500\ K$$

D
$$3000$$ and $$3500\ K$$

Solution
Question 5
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Which of the following statements is wrong?

A
Evaporation is a spontaneous process.

B
Evaporation is a surface phenomenon.

C
Vapour pressure decreases with increase of temperature.

D
The vapour pressure of a solution is always less than the vapour pressure of a pure solvent.

Solution
Question 6
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Which of the following is not true about a reversible reaction?

A
The reaction does not proceed to completion

B
It cannot be influenced by a catalyst

C
Number of moles of reactants and products is always equal

D
It can be attained only in a closed container
Question 7
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$$2{H}_{2(g)}+{O}_{2(g)}\rightarrow 2{H}_{2}{O}_{(l)};\Delta H=-ve$$ and $$\Delta G=-ve$$. Then the reaction is

A
Spontaneous and instantaneous

B
Spontaneous and endothermic

C
Spontaneous and slow

D
Non spontaneous and slow

Solution
Question 8
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Which of the following expression for an irreversible process:

A
$$d{S}_{Total}> \cfrac{dq}{T}$$

B
$$d{S}_{Total}= \cfrac{dq}{T}$$

C
$$d{S}_{Total}< \cfrac{dq}{T}$$

D
$$d{S}_{Total}= \cfrac{dU}{T}$$
Question 9
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In standard state the non spontaneous reaction among the following is:

A
melting of ice

B
natural radioactivity

C
freezing of water

D
rusting of iron

Solution

Ans$$C$$- freeging of water
water exists in liquid state naturally at standard state $${ 25 }^{ \circ }c=298k$$. Hence freezing of $${ H }_{ 2 }O$$ at 298k is non-spontaneous as ice will absorb heat from surroundings thereby gets converted to the liquid state as it is a natural process of is irreversible.
Question 10
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Answer the question based on the diagram involving $$1$$ mole of ideal gas.
Process $$A\rightarrow B$$ represents:

A
isobaric

B
isochoric

C
isothermal

D
adiabatic

Solution

Solution:- (B) isochoric process
In process $$A \rightarrow B$$, as the volume is constant, thus the process represents isochoric process.