Thermodynamics Test

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Thermodynamics Test - 24

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Question 1
1 / -0

$$10\ g$$ of liquid at $$300\ K$$ are heated to $$350\ K$$. The liquid absorbs $$6\ kcal$$. What is the specific heat of the liquid (in $$cal/g^{\circ}C)$$?

A
$$6$$

B
$$12$$

C
$$60$$

D
$$120$$

E
$$600$$

Solution

Answer(B)
liquid is heated from 300k to 350k so temperature difference $$=$$$$50K$$
so $$C$$$$=$$$$Q/(m*T)$$$$=$$$$6000/(10*50)$$$$=$$$$12cal/gC$$
Question 2
1 / -0

Which set of the conditions given below guarantees that a reaction will be spontaneous?

A
$$\Delta H(+)$$ and $$\Delta S(-)$$

B
$$\Delta H(-)$$ and $$\Delta S(+)$$

C
$$\Delta H(+)$$ and $$\Delta S(+)$$ at low temperature

D
$$\Delta H(-)$$ and $$\Delta S(-)$$ at high temperature

E
$$\Delta G(+)$$

Solution

For a spontaneous reaction, $$\displaystyle \Delta G < 0$$
Also, $$\displaystyle \Delta G = \Delta H - T \Delta S$$
Hence, when $$\displaystyle \Delta H < 0$$ and $$\displaystyle \Delta S > 0$$, $$\displaystyle \Delta G < 0$$, and the reaction will become spontaneous.
Question 3
1 / -0

Which is the amount of energy that must be added to raise the temperature of 1 gram of a substance by $$\displaystyle { 1 }^{ \circ }C$$?

A
Enthalpy change

B
Entropy change

C
Gibbs free energy change

D
Activation energy

E
Specific heat capacity

Solution

The specific heat (also called specific heat capacity) is the amount of heat required to change a unit mass (or unit quantity, such as mole) of a substance by one degree in temperature.
Question 4
1 / -0

Which of the following condition guarantee a spontaneous reaction?

A
Positive $$\displaystyle \Delta H$$, Positive $$\displaystyle \Delta S$$

B
Positive $$\displaystyle \Delta H$$, Negative $$\displaystyle \Delta S$$

C
Negative $$\displaystyle \Delta H$$, Negative $$\displaystyle \Delta S$$

D
Negative $$\displaystyle \Delta H$$, Positive $$\displaystyle \Delta S$$

E
None of the above

Solution

ΔG=ΔH-TΔS, for a reaction to be spontaneous ΔG, should be negative.
It can take place only when both terms in RHS is negative. therefore ΔH should be negative and
ΔS should be positive.
Question 5
1 / -0

$$I$$. The energy content of reactants in a chemical reaction must be equal to the energy content of the products.
$$II$$. Energy is conserved in chemical processes.

A
Statement $$I$$ is true, Statement $$II$$ is true and is a correct explanation of the phenomena described in $$I$$

B
Statement $$I$$ is true, Statement $$II$$ is false

C
Statement $$I$$ is false, Statement $$II$$ is true

D
Statement $$I$$ is false, Statement $$II$$ is false

Solution

According to law of conservation of energy, energy can neither be created, nor be destroyed, it can be changed from one form to another.
Therefore, energy is conserved in a chemical change/processes, i.e; the energy content of reactants in a chemical reaction must be equal to energy content of the products.
Question 6
1 / -0

Which portion of the heating curve for water shown would there be ONLY liquid water present?

A
$$A-B$$

B
$$B-C$$

C
$$C-D$$

D
$$D-E$$

Solution

C-D is the portion where liquid water is present in heating curve.
Question 7
1 / -0

Statement I: A reaction with a positive enthalpy and a negative entropy will be spontaneous
BECAUSE
Statement II: The Gibbs free energy for a spontaneous reaction is negative

A
Statement $$1$$ and Statement $$2$$ are correct and Statement 2 is the correct explanation of Statement $$1$$

B
Both the 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

We know the formula $$\Delta G$$$$=$$$$\Delta H$$$$-$$$$T$$$$\Delta S$$
Positive enthalpy means $$\Delta H$$ is $$+ve$$.
The second term on the right hand side of the equation is already $$-ve$$. If we take a negative entropy again, the second term on the right hand side will become positive. Hence the total value of $$\Delta G$$ will be positive. But Gibb's free energy for a spontaneous reaction can't be positive. Hence statement 1 is not correct.
Statement 2 is correct. Gibb's free energy for a spontaneous reaction is negative.
Option D is the correct answer.
Question 8
1 / -0

At what point of the heating curve are intermolecular forces at their greatest level?

A
$$1$$

B
$$2$$

C
$$3$$

D
$$4$$

Solution

From the heating curve, we can observe that there are two regions of constant temperature, namely 2 and 3. This means that the heat supplied is not being used to raise the temperature but is used to overcome the intermolecular forces holding the particles together. Hence there must be two phase change taking place. Thus, we can conclude that state 1 is solid whereas state 2 is liquid. Since a solid has the highest intermolecular forces, the correct answer is 1
Question 9
1 / -0

How much energy is needed to melt $$100g$$ of water?
$$\Delta {H}_{v}=540\ cal/g$$
$$\Delta {H}_{f}=80\ cal/g$$
$${C}_{water}=1\ cal/{g}^{o}C$$

A
$$640cal$$

B
$$8000cal$$

C
$$54,000cal$$

D
$$180cal$$

Solution

Latent heat of fusion $$=80cal/g$$
To melt 100gm ,we have $$(80)(100)=8000$$ calories of heat.
Question 10
1 / -0

Which portion of the heating curve for water shown above would there be both liquid and solid water present?

A
$$A-B$$

B
$$B-C$$

C
$$C-D$$

D
$$D-E$$

Solution

B-C is the region where both ice and water are present .
In this region both ice and water are in equilibrium.

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Thermodynamics Test - 24

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Thermodynamics Test - 24

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Question 1

$$6$$

$$12$$

$$60$$

$$120$$

$$600$$

Solution

Question 2

$$\Delta H(+)$$ and $$\Delta S(-)$$

$$\Delta H(-)$$ and $$\Delta S(+)$$

$$\Delta H(+)$$ and $$\Delta S(+)$$ at low temperature

$$\Delta H(-)$$ and $$\Delta S(-)$$ at high temperature

$$\Delta G(+)$$

Solution

Question 3

Enthalpy change

Entropy change

Gibbs free energy change

Activation energy

Specific heat capacity

Solution

Question 4

Positive $$\displaystyle \Delta H$$, Positive $$\displaystyle \Delta S$$

Positive $$\displaystyle \Delta H$$, Negative $$\displaystyle \Delta S$$

Negative $$\displaystyle \Delta H$$, Negative $$\displaystyle \Delta S$$

Negative $$\displaystyle \Delta H$$, Positive $$\displaystyle \Delta S$$

None of the above

Solution

Question 5

Statement $$I$$ is true, Statement $$II$$ is true and is a correct explanation of the phenomena described in $$I$$

Statement $$I$$ is true, Statement $$II$$ is false

Statement $$I$$ is false, Statement $$II$$ is true

Statement $$I$$ is false, Statement $$II$$ is false

Solution

Question 6

$$A-B$$

$$B-C$$

$$C-D$$

$$D-E$$

Solution

Question 7

Statement $$1$$ and Statement $$2$$ are correct and Statement 2 is the correct explanation of Statement $$1$$

Both the 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 8

$$1$$

$$2$$

$$3$$

$$4$$

Solution

Question 9

$$640cal$$

$$8000cal$$

$$54,000cal$$

$$180cal$$

Solution

Question 10

$$A-B$$

$$B-C$$

$$C-D$$

$$D-E$$

Solution

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