Thermodynamics Test

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Thermodynamics Test - 30

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Weekly Quiz Competition

Question 1
1 / -0

A large positive value of $$\Delta { G }$$ corresponds to which of these?

A
Small positive $$K$$

B
Small negative $$K$$

C
Large positive $$K$$

D
Large negative $$K$$

Solution

$$\Delta G={ \Delta G }^{ 0 }+RTlnK$$
At equilibrium, $$\Delta G=0$$
$$\therefore \quad { \Delta G }^{ 0 }=-RTlnK$$
$$\therefore \quad K={ e }^{ -{ \Delta G }^{ 0 }/RT }=\frac { 1 }{ { e }^{ { \Delta G }^{ 0 }/RT } } >0$$
Therefore, a large positive value of $$\Delta G$$ corresponds to small positive K.
Question 2
1 / -0

Under which circumstances would the free energy change for a reaction be relatively temperature independent?

A
$$\Delta { H }^{ o }$$ is negative

B
$$\Delta { H }^{ o }$$ is positive

C
$$\Delta { S }^{ o }$$ has a large positive value

D
$$\Delta { S }^{ o }$$ has a small magnitude

Solution

$${ \left( \Delta { G } \right) }=$$$${ \left( \Delta { H } \right) }-$$$$T$$$${ \left( \Delta { S } \right) }$$
$$\text{From the above equation we can say for being independence of temperature }$$$${ \left( \Delta { S } \right) }$$$$\text{ has to become small in magnitude or almost zero.}$$
Question 3
1 / -0

$$2Zn+{ O }_{ 2 }\longrightarrow 2ZnO;\Delta { G }^{ o }=-616J..(i)\quad $$
$$2Zn+2S\longrightarrow 2ZnS;\Delta { G }^{ o }=-293J...(ii)$$
$$2S+2{ O }_{ 2 }\longrightarrow 2S{ O }_{ 2 }(g);\Delta { G }^{ o }=-408J..(iii)$$
$$\Delta { G }^{ o }$$ for the following reaction:
$$2ZnS+3{ O }_{ 2 }\longrightarrow 2ZnO+2{ SO }_{ 2 }$$ would be:

A
$$-731J$$

B
$$-1317J$$

C
$$+731J$$

D
$$+1317J$$

Solution

$$\Delta { G }^{ o }=2\Delta {G}_{ZnO}^{o}+2\Delta {G}_{{SO}_{2}}^{o}-2\Delta {G}_{ZnS}^{o}$$
$$=[-616-408]-[-293]$$
$$=-731J$$
Question 4
1 / -0

The value of $$\log _{ 10 }{ K } $$ for a reaction
$$A\rightleftharpoons B$$ is____________.
Given $${ \Delta }_{ r }{ H }_{ 298K }^{ o }=-54.07kJ{ mol }^{ -1 },{ \Delta }_{ r }{ S }_{ 298K }^{ o }=10J{ K }^{ -1 }{ mol }^{ -1 },R=8.314J{ K }^{ -1 }{ mol }^{ -1 }$$

A
$$5$$

B
$$10$$

C
$$95$$

D
$$100$$

Solution
Question 5
1 / -0

Given that:
$$2C(s)+2{ O }_{ 2 }(g)\longrightarrow 2C{ O }_{ 2 }(g);\Delta H=-787kJ...(i)$$
$${ H }_{ 2 }(g)+\cfrac { 1 }{ 2 } { O }_{ 2 }(g)\longrightarrow { H }_{ 2 }O(l);\Delta H=-286kJ...(ii)$$
$${ C }_{ 2 }{ H }_{ 2 }(g)+\cfrac { 5 }{ 2 } { O }_{ 2 }(g)\longrightarrow 2C{ O }_{ 2 }(g)+3{ H }_{ 2 }O(l)....(iii)$$
$$\Delta H=-1301kJ$$
Heat formation of acetylene is:

A
$$-1802kJ$$

B
$$+1802kJ$$

C
$$-800kJ$$

D
$$+228kJ$$

Solution

Required equation is:
$$2C(s)+{ H }_{ 2 }(g)\longrightarrow { C }_{ 2 }{ H }_{ 2 }(g)$$
$$eq.(i)+eq.(ii)-eq.(iii)$$ gives
$$\Delta H=+228kJ$$
Question 6
1 / -0

The enthalpy changes for two reactions are given by the equations:
$$2Cr(s)+1\cfrac { 1 }{ 2 } { O }_{ 2 }(g)\longrightarrow { Cr }_{ 2 }{ O }_{ 3 }(s);\Delta H=-1130kJ$$
$$C(s)+\cfrac { 1 }{ 2 } { O }_{ 2 }(g)\longrightarrow CO(g);\Delta H=-110kJ$$
What is the enthalpy change, in $$kJ$$, for the reaction?
$$3C(s)+{ Cr }_{ 2 }{ O }_{ 3 }(s)\longrightarrow 2Cr(s)+3CO(g)$$

A
$$-1460kJ$$

B
$$-800kJ$$

C
$$+800kJ$$

D
$$+1020kJ$$

E
$$+1460kJ$$

Solution

$${ Cr }_{ 2 }{ O }_{ 3 }(s)\longrightarrow 2Cr(s)+\cfrac { 3 }{ 2 } { O }_{ 2 }(g);\Delta H=+1130kJ$$
$$3C(s)+\cfrac { 3 }{ 2 } { O }_{ 2 }(g)\longrightarrow 3CO(g);\Delta H=-330kJ$$
Adding both equaitons $$\Delta H=+800kJ$$
Question 7
1 / -0

The enthalpy change for two reactions are given by the equations:
$$2Cr(s)+\cfrac { 3 }{ 2 } { O }_{ 2 }(g)\longrightarrow { Cr }_{ 2 }{ O }_{ 3 }(s);\Delta H=-1130kJ$$
$$C(s)+\cfrac { 1 }{ 2 } { O }_{ 2 }(g)\longrightarrow CO(g);\Delta H=-110kJ$$
What is the enthalpy change in $$kJ$$ for the following reaction?
$$3C(s)+{ Cr }_{ 2 }{ O }_{ 3 }(s)\longrightarrow 2Cr(s)+3CO(g)$$

A
$$-1460kJ$$

B
$$-1800kJ$$

C
$$+800kJ$$

D
$$-1020kJ$$

E
$$+1460kJ$$

Solution

$$3C(s)+\cfrac { 3 }{ 2 } { O }_{ 2 }(g)\longrightarrow 3CO(g);\ \Delta H=-330kJ\quad $$
$${ Cr }_{ 2 }{ O }_{ 3 }(s)\longrightarrow 2Cr(s)+\cfrac { 3 }{ 2 } { O }_{ 2 }(g);\ \Delta H=+1130kJ\quad $$

On adding above two reaction:

$$3C(s)+{ Cr }_{ 2 }{ O }_{ 3 }(s)\longrightarrow 2Cr(s)+3CO(g);\ \Delta H=-330+1130=800\ kJ$$
Question 8
1 / -0

Given that:
$$2Fe(s)+\cfrac { 3 }{ 2 } { O }_{ 2 }(g)\longrightarrow { Fe }_{ 2 }{ O }_{ 3 }(s);\Delta H=-193.4kJ...(i)$$
$$Mg(s)+\cfrac { 1 }{ 2 } { O }_{ 2 }(g)\longrightarrow MgO(s);\Delta H=-140.2kJ....(ii)$$
What is $$\Delta H$$ of the reaction?
$$3Mg+{ Fe }_{ 2 }{ O }_{ 3 }\longrightarrow 3MgO+2Fe$$

A
$$-227.2kJ$$

B
$$-237.3kJ$$

C
$$2227.2kJ$$

D
$$-257.3kJ$$

Solution

Eq.$$(ii)$$ multiplied by $$3$$,
$$3Mg+{ Fe }_{ 2 }{ O }_{ 3 }\longrightarrow 3MgO;\Delta H=-420.6kJ...(iii)$$
$$2Fe(s)+\cfrac { 3 }{ 2 } { O }_{ 2 }(g)\longrightarrow { Fe }_{ 2 }{ O }_{ 3 }(s);\Delta H=-193.4kJ...(i)$$
Subtracting $$(i)$$ from $$(iii)$$
$$3Mg+{ Fe }_{ 2 }{ O }_{ 3 }\longrightarrow 3MgO+2Fe\quad \Delta H=-420.6-(-193.4)$$
$$=-227.2kJ$$
Question 9
1 / -0

A 100.0g ice cube at 0.0°C is placed in 650g of water at 25°C. What is the final temperature of the mixture?

A
$$10^0C$$

B
$$11^0C$$

C
$$12^0C$$

D
$$13^0C$$

Solution
Question 10
1 / -0

For spontaneous process:

A
$$\Delta { S }_{ total }=0$$

B
$$\Delta { S }_{ total }>0$$

C
$$\Delta { S }_{ total }<0$$

D
none of these

Solution

$$\text{Change in entropy is always positive.}$$

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Thermodynamics Test - 30

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Thermodynamics Test - 30

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Question 1

Small positive $$K$$

Small negative $$K$$

Large positive $$K$$

Large negative $$K$$

Solution

Question 2

$$\Delta { H }^{ o }$$ is negative

$$\Delta { H }^{ o }$$ is positive

$$\Delta { S }^{ o }$$ has a large positive value

$$\Delta { S }^{ o }$$ has a small magnitude

Solution

Question 3

$$-731J$$

$$-1317J$$

$$+731J$$

$$+1317J$$

Solution

Question 4

$$5$$

$$10$$

$$95$$

$$100$$

Solution

Question 5

$$-1802kJ$$

$$+1802kJ$$

$$-800kJ$$

$$+228kJ$$

Solution

Question 6

$$-1460kJ$$

$$-800kJ$$

$$+800kJ$$

$$+1020kJ$$

$$+1460kJ$$

Solution

Question 7

$$-1460kJ$$

$$-1800kJ$$

$$+800kJ$$

$$-1020kJ$$

$$+1460kJ$$

Solution

Question 8

$$-227.2kJ$$

$$-237.3kJ$$

$$2227.2kJ$$

$$-257.3kJ$$

Solution

Question 9

$$10^0C$$

$$11^0C$$

$$12^0C$$

$$13^0C$$

Solution

Question 10

$$\Delta { S }_{ total }=0$$

$$\Delta { S }_{ total }>0$$

$$\Delta { S }_{ total }<0$$

none of these

Solution

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