Thermodynamics Test

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Thermodynamics Test - 22

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Weekly Quiz Competition

Question 1
1 / -0

What wiII be the heat of formation of methane, if the heat of combustion of carbon is $$'-x' kJ$$, heat of formation of water is $$'-y' kJ$$ and heat of combustion of methane is $$'z' kJ$$?

A
$$(-x - y + z) kJ$$

B
$$(-z -x + 2y) kJ$$

C
$$(-x - 2y - z) kJ$$

D
$$(-x -2y + z) kJ$$

Solution

From given data, we have
$$C + O_{2} \rightarrow CO_{2} - x\ kJ ...... (i)$$
$$H_{2} + \dfrac {1}{2} O_{2} \rightarrow H_{2} O - y\ kJ ...... (ii)$$
$$CH_{4} + 2O_{2} \rightarrow CO_{2} + 2H_{2}O + z\ kJ ..... (iii)$$
The required equation is
$$C + 2H_{2} \rightarrow CH_{4} + Q$$
where Q is heat of combustion of $$CH_4$$
To get the required equation, operate
$$(i) + 2\times (ii) - (iii)$$
$$C + 2H_{2} \rightarrow CH_{4} + [(-x) + (-2y) - (-z)]$$
Thus, heat of formation of methane is
$$(-x -2y + z) kJ$$
Question 2
1 / -0

For the reaction of one mole of zinc dust with one mole of sulphuric acid in a bomb calorimeter, $$\triangle U$$ and $$w$$ corresponds to:

A
$$\triangle U < 0, w = 0$$

B
$$\triangle U < 0, w < 0$$

C
$$\triangle U > 0, w = 0$$

D
$$\triangle U > 0, w > 0$$

Solution

$$Zn + H_{2}SO_{4} = ZnSO_{4} + H_{2}$$

In bomb calorimeter, there is no expansion in volume, so, work done will be zero.

This reaction is exothermic. So, some heat will be evolved which will result in lowering of internal energy.

Hence,$$\triangle U < 0$$ & $$w = 0$$.
Question 3
1 / -0

If $$Q$$ and $$W$$ represent the heat supplied to the system and the work done on the system respectively, then the first law of thermodynamics can be written as:

A
$$ Q=\Delta U+ W$$

B
$$Q=\Delta U- W$$

C
$$Q=W-\Delta U$$

D
None of these

Solution

From First law of thermodynamics,
$$\Delta U=Q+ W$$

$$\because$$ Heat supplied to the system so $$ Q\rightarrow $$ Positive
and work is done on the system so $$ W \rightarrow$$ Positive

Hence, $$ Q=\Delta U-W$$
Question 4
1 / -0

Gibbs- Helmholtz equation is:

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

B
$$\Delta G = - T\Delta H - \Delta S$$

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

D
$$\Delta G = -T\Delta H + \Delta S$$

Solution

Gibbs-Helmholtz Equation
$$ \Delta G = \Delta H - T \Delta S $$
Measure
of heat
in the
reaction

$$ \blacksquare $$ In chemical reactions, reactions absorb
energy to break bonds

$$ \blacksquare $$ Energy is then released when bonds from
between rearranged atoms of the product
Question 5
1 / -0

What is the characteristic of a material which undergo spontaneous combustion?

A
High calorific value

B
High vapour pressure

C
Low ignition temperature

D
All of the above

Solution

Spontaneous combustion is a byproduct of spontaneous heating, which occurs when a material increases in temperature without drawing heat from its surroundings. Such materials have a low ignition temperature. If the material reaches its ignition temperature, spontaneous ignition or combustion occurs.
Examples of materials that are prone to spontaneous combustion include oily rags, hay, and other agricultural products.
Question 6
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The enthalpy of formation of $$CO_{(g)}, CO_{2(g)}, N_{2}O_{(g)}$$ and $$N_{2}O_{4(g)}$$ is $$-110, -393, +811$$ and $$10\ kJ/ mol$$ respectively. For the reaction, $$N_{2}O_{4(g)} + 3CO_{(g)} \rightarrow N_{2}O_{(g)} + 3CO_{2(g)} \cdot \triangle H_{r} (kJ/mol)$$ is

A
$$-212$$

B
$$+212$$

C
$$+48$$

D
$$-48$$

Solution

$$N_{2}O_{4(g)} + 3CO_{(g)} \rightarrow N_{2}O_{(g)} + 3CO_{2(g)}$$
$$\triangle H_{reaction} = \sum_{\text {Heat of formation of products}} - \sum_{\text {Heat of formation of reactants}}$$
$$\triangle H_{reaction} = [\triangle H_{f}N_{2}O + 3\times \triangle H_{f}CO_{2}] - [\triangle H_{f} N_{2}O_{4} + 3\times \triangle H_{f}CO]$$
$$\triangle H_{r} = [+811 + 3(-393)] - [10 + 3(-110)]$$
$$= [811 - 1179] - [-320] = -368 + 320$$
$$= -48\ kJ/mol$$
Question 7
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According to the first law of thermodynamics which of the following quantities represents the change in a state function?

A
$$\displaystyle { q }_{ reV }$$

B
$$\displaystyle { q }_{ reV }-{ W }_{ reV }$$

C
$$\displaystyle \frac { { q }_{ reV } }{ { W }_{ reV } } $$

D
$$\displaystyle { q }_{ reV }+{ W }_{ reV }$$

Solution

A state function is a property whose value does not depend on the path taken to reach that specific value.
Internal energy is an example of state function.
$$\Delta E={ q }_{ rev }+{ w }_{ rev }$$
Whereas heat and work done are not state functions.
Question 8
1 / -0

Statement 1 : Candles can be safely stored at room temperature, even though their reaction with air is spontaneous at room temperature.
Statement 2 : The reaction that takes place when a candle is burned involves a decrease in entropy.

A
Both Statement 1 and Statement 2 are correct and Statement 2 is the correct explanation of Statement 1.

B
Both Statement 1 and Statement 2 are correct and Statement 2 is not the correct explanation of Statement 1.

C
Statement 1 is correct but Statement 2 is not correct.

D
Statement 1 is not correct but Statement 2 is correct.

E
Both the Statement 1 and Statement 2 are not correct.

Solution

Statement : If equal masses of sodium metal and chlorine gas are allowed to react, some sodium will be left over after all the chlorine is used up.
The molar mass of chlorine is higher than the molar mass of sodium. Hence, for equal masses, the number of moles of chlorine will be smaller than the number of moles of sodium.
Statement 2 : The reaction required twice as many atoms of sodium as the molecules of chlorine.
$$\displaystyle 2Na + Cl_2 \rightarrow 2NaCl$$
Statement 1 is correct but Statement 2 is not correct.

Question 9

1 / -0

Match list I with list II and select the correct answer using the codes given below the lists:

List I	List II
A.$${ \left( \cfrac { \delta G }{ \delta P } \right) }_{ T }\quad $$	1. $${ \mu }_{ H }$$
B.$${ \left( \cfrac { \delta G }{ \delta T } \right) }_{ P }$$	2. $$T$$
C.$${ \left( \cfrac { \delta H }{ \delta S } \right) }_{ P }$$	3. $$-S$$
D. $${ \left( \cfrac { \delta T }{ \delta P } \right) }_{ H }$$	4. $$P$$
	5. $$V$$

$$A-5, B-1, C-2, D-4$$

$$A-5, B-3, C-2, D-4$$

$$A-3, B-5, C-2, D-1$$

$$A-5, B-3, C-2, D-1$$

Solution

From thermodynamics $$dG=VdP-SdT$$
At constant $$T,dT=0$$ so that $${ \left( \cfrac { \delta G }{ \delta P } \right) }_{ T }\quad =V$$
At cosntant $$P,dP=0$$ so that $${ \left( \cfrac { \delta G }{ \delta T } \right) }_{ P }=-S$$
Also $${\mu}_{H}={ \left( \cfrac { \delta T }{ \delta P } \right) }_{ H }$$

Question 10
1 / -0

For the reaction, $$X_2Y_4(l) \longrightarrow 2XY_2(g)$$ at 300 K, the values of $$\Delta U$$ and $$\Delta S$$ are 2 kcal and 20 cal $$K^{-1}$$ respectively. The value of $$\Delta G$$ for the reaction is

A
- 3400 cal

B
3400 cal

C
- 2800 cal

D
2000 cal

Solution

$$\Delta H=\Delta U+\Delta n_gRT=2000+2\times2\times300=3200\ cal$$
$$\displaystyle \Delta G = \Delta H - T\Delta S = 3200 - 300 \times 20 = -2800 \: cal $$

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Thermodynamics Test - 22

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Thermodynamics Test - 22

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Question 1

$$(-x - y + z) kJ$$

$$(-z -x + 2y) kJ$$

$$(-x - 2y - z) kJ$$

$$(-x -2y + z) kJ$$

Solution

Question 2

$$\triangle U < 0, w = 0$$

$$\triangle U < 0, w < 0$$

$$\triangle U > 0, w = 0$$

$$\triangle U > 0, w > 0$$

Solution

Question 3

$$ Q=\Delta U+ W$$

$$Q=\Delta U- W$$

$$Q=W-\Delta U$$

None of these

Solution

Question 4

$$\Delta G = T\Delta H + \Delta S$$

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

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

$$\Delta G = -T\Delta H + \Delta S$$

Solution

Question 5

High calorific value

High vapour pressure

Low ignition temperature

All of the above

Solution

Question 6

$$-212$$

$$+212$$

$$+48$$

$$-48$$

Solution

Question 7

$$\displaystyle { q }_{ reV }$$

$$\displaystyle { q }_{ reV }-{ W }_{ reV }$$

$$\displaystyle \frac { { q }_{ reV } }{ { W }_{ reV } } $$

$$\displaystyle { q }_{ reV }+{ W }_{ reV }$$

Solution

Question 8

Both Statement 1 and Statement 2 are correct and Statement 2 is the correct explanation of Statement 1.

Both Statement 1 and Statement 2 are correct and Statement 2 is not the correct explanation of Statement 1.

Statement 1 is correct but Statement 2 is not correct.

Statement 1 is not correct but Statement 2 is correct.

Both the Statement 1 and Statement 2 are not correct.

Solution

Question 9

$$A-5, B-1, C-2, D-4$$

$$A-5, B-3, C-2, D-4$$

$$A-3, B-5, C-2, D-1$$

$$A-5, B-3, C-2, D-1$$

Solution

Question 10

- 3400 cal

3400 cal

- 2800 cal

2000 cal

Solution

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