Theromodynamics and Thermochemistry Test

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Theromodynamics and Thermochemistry Test - 1

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Weekly Quiz Competition

Question 1
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The first law of thermodynamics is only

A
The law of conservation of energy

B
The law of conservation of mass

C
The law of conservation of momentum

D
Both (a) and (b)

Solution

First low of thermodynamics is also known as Law of conservation of mass and energy.
Question 2
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A mixture of two moles of carbon monoxide and one mole of oxygen, in a closed vessel is ignited to convert the carbon monoxide to carbon dioxide. If ΔH is the enthalpy change and ΔE is the change in internal energy, then

A
ΔH > ΔE

B
ΔH < ΔE

C
ΔH = ΔE

D
The relationship depends on the capacity of the vessel

Solution

Formation of CO₂from CO is an exothermic reaction; heat is evolved from the system, i.e., energy is lowered. Thus, exothermic reactions occur spontaneously on account of decrease in enthapy of system. Thus, ΔE > ΔH.
Question 3
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The relation between ΔE and ΔH is

A
ΔH = ΔE - P ΔV

B
ΔH = ΔE + P ΔV

C
ΔE = ΔV + P ΔH

D
ΔE = ΔH + P ΔV

Solution

ΔH = ΔE + P ΔV.
Question 4
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For the reaction of one mole of zinc dust with one mole of sulphuric acid in a bomb calorimeter, ΔU and w correspond to

A
ΔU < 0, w = 0

B
ΔU = 0, w < 0

C
ΔU > 0, w = 0

D
ΔU < 0, w > 0

Solution

Bomb calorimeter is commonly used to find the heat of combustion of organic substances which consists of a sealed combustion chamber, called a bomb. If a process is run in a sealed container then no expansion or compression is allowed, so w = 0 and ΔU = q.

ΔU < 0, w = 0
Question 5
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For the reaction N₂ + 3H2 ⇌ 2NH3 ; ΔH =

A
ΔE - RT

B
ΔE - 2RT

C
ΔE + RT

D
ΔE + 2RT

Solution

ΔH = ΔE + ΔnRT

Since Δn = - 2

Than ΔH = ΔE - 2RT.
Question 6
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If ΔH is the change in enthalpy and ΔE the change in internal energy accompanying a gaseous reaction

A
ΔH is always greater than ΔE

B
ΔH < ΔE only if the number of moles of the products is greater than the number of the reactants

C
ΔH is always less than ΔE

D
ΔH < ΔE only if the number of moles of the products is less than the number of moles of the reactants

Solution

If Δn = -ve than ΔH < ΔE.
Question 7
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Hess's law of constant heat summation in based on

A
E = mc²

B
Conservation of mass

C
First law of thermodynamics

D
None of the above

Solution

Hess’s law is an application of first law of thermodynamics .
Question 8
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Consider the reaction : N₂+ 3H₂→ 2 NH₃carried out at constant temperature and pressure. If ΔH and ΔU are the enthalpy and internal energy changes for the reaction, which of the following expression is true

A
ΔH = 0

B
ΔH = ΔU

C
ΔH < ΔU

D
ΔH > ΔU

Solution

At constant P or T

ΔH = ΔU + ΔnRT ⇒ Δn = n_p- n_R= 2 - 4 = - 2

∴ ΔH < ΔU.
Question 9
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Enthalpy for the reaction C + O₂→ CO₂ is

A
Positive

B
Negative

C
Zero

D
None

Solution

It is a combustion reaction, ΔH = - ve.

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Theromodynamics and Thermochemistry Test - 1

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Question 1

The law of conservation of energy

The law of conservation of mass

The law of conservation of momentum

Both (a) and (b)

Solution

Question 2

ΔH > ΔE

ΔH < ΔE

ΔH = ΔE

The relationship depends on the capacity of the vessel

Solution

Question 3

ΔH = ΔE - P ΔV

ΔH = ΔE + P ΔV

ΔE = ΔV + P ΔH

ΔE = ΔH + P ΔV

Solution

Question 4

ΔU < 0, w = 0

ΔU = 0, w < 0

ΔU > 0, w = 0

ΔU < 0, w > 0

Solution

Question 5

ΔE - RT

ΔE - 2RT

ΔE + RT

ΔE + 2RT

Solution

Question 6

ΔH is always greater than ΔE

ΔH < ΔE only if the number of moles of the products is greater than the number of the reactants

ΔH is always less than ΔE

ΔH < ΔE only if the number of moles of the products is less than the number of moles of the reactants

Solution

Question 7

E = mc2

Conservation of mass

First law of thermodynamics

None of the above

Solution

Question 8

ΔH = 0

ΔH = ΔU

ΔH < ΔU

ΔH > ΔU

Solution

Question 9

Positive

Negative

Zero

None

Solution

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E = mc²