Test: Thermodynamics And Thermochemistry - 1


20 Questions MCQ Test Physical Chemistry | Test: Thermodynamics And Thermochemistry - 1


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QUESTION: 1

 Heat produced in calories by the combustion of one gram of carbon is called:

Solution:

It is the definition of calorific value.

QUESTION: 2

The temperature of the system decreases in an:

Solution:
  • The temperature of the system decreases in an adiabatic expansion.
  • In isothermal process, temperature remains same.
  • The temperature of the system increases in an adiabatic compression.
QUESTION: 3

For the isothermal expansion of an ideal gas:

Solution:
  • An isothermal process is a change of a system, in which the temperature remains constant. For an ideal gas during an isothermal expansion the enthalpy, as well as internal energy, remains constant.
  • During isothermal expansion of an ideal gas, ΔE = 0, ΔT=0
  • From the definition of enthalpy,
    H=E+PV
    or ΔH=ΔE+Δ(PV)
    or ΔH=ΔE+Δ(nRT) {Since, PV=nRT for an ideal gas}
    or ΔH=ΔE + nRΔT
    or ΔH=0
QUESTION: 4

In an isochoric process, the increased internal energy is:

Solution:

In an isochoric process, ΔV=0.

Hence, work done PΔV = W = 0.

So, ΔE = q+0.

Hence, the increase in internal energy will be equal to heat absorbed by the system.

QUESTION: 5

Internal energy is an example of:

Solution:

Internal energy, enthalpy, and entropy are state quantities because they describe quantitatively an equilibrium state of a thermodynamic system, irrespective of how the system arrived in that state.

QUESTION: 6

The process in which no heat enters or leaves the system is termed as:

Solution:

An adiabatic process occurs without transfer of heat or mass of substances between a thermodynamic system and its surroundings. In an adiabatic process, energy is transferred to the surroundings only as work.

QUESTION: 7

If in a container neither mass and nor heat exchange occurs then it constitutes a ______.

Solution:

An isolated system neither shows exchange of heat nor matter with surroundings.

QUESTION: 8

Which of the following is true for an adiabatic process:

Solution:

A process that does not involve the transfer of heat or matter into or out of a system, so that ΔQ = 0, is called an adiabatic process and such a system is said to be adiabatically isolated.

QUESTION: 9

Among the following, intensive property is:

Solution:

An intensive property is a property of matter that does not change as the amount of matter changes. It is a bulk property, which means it is a physical property that is not dependent on the size or mass of a sample. In contrast, an extensive property is one that does depend on sample size.

QUESTION: 10

For the reaction of one mole of zinc dust with one mole of sulphuric acid in a bomb calorimeter, ΔU and W correspond to:

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 ∆U = q.

∆U < 0, w = 0

QUESTION: 11

Which of the following expressions represent the first law of thermodynamics:

Solution:
  • The first law of thermodynamics is a version of the law of conservation of energy, adapted for thermodynamic systems.
  • The law of conservation of energy states that the total energy of an isolated system is constant; energy can be transformed from one form to another, but can be neither created nor destroyed.
  • The first law is often formulated
    ΔE = Q + W            
QUESTION: 12

At 270C one mole of an ideal gas is compressed isothermally and reversibly from a pressure of 2 atm to 10 atm. The value of ΔE and q are (R = 2):

Solution:

Isothermally (at constant temperature) and reversible work.

w = -2.303nrt log(P1/P2)

at constant temperature , ΔE = 0
ΔE = Q + W,

 

Q = −W = −965.84 cal

QUESTION: 13

The heat required to raise the temperature of a body by 1K is called:

Solution:

The heat required to raise the temperature of a body by 1 K is called thermal capacity. In other words, when q is the heat supplied to the body and the temperature rises by 1 K, then the thermal capacity of body is q.

QUESTION: 14

Which of the following is true for the reaction H2​O(l)​ ⇋ H2​O(g)​ at 1000C at one atmosphere:

Solution:

H2​O(l) ​⇋ H2​O(g)​

As we know that, at equilibrium, ΔG=0

∴ΔH−TΔS=0

⇒ΔH=TΔS

QUESTION: 15

Identify the correct statement regarding entropy:

Solution:

According to the third law of thermodynamics (regarding the properties of systems in equilibrium at absolute zero temperature): 

The entropy of a perfect crystal at absolute zero is exactly equal to zero. At absolute zero (zero kelvin), the system must be in a state with the minimum possible energy, and the above statement of the third law holds true provided that the perfect crystal has only one minimum energy state.

QUESTION: 16

Maximum entropy will be in which of the following:

Solution:

  Entropy of gases is highest.

QUESTION: 17

If enthalpies of formation C2H4 (g), CO2 (g) and H2O (l) at 2500C and 1 atm. pressure be 52, –394 and –286 KJ mol–1 respectively. The enthalpy of combustion of C2H4 (g) will be:

Solution:

QUESTION: 18

Heat of neutralization of strong acid and weak base is:

Solution:
  • Heat of neutralization of strong acid and weak base is less than 13.7 kcal/mol because some of energy used in dissociation of weak base.
  • For strong acid and strong base heat of neutralization has constant values 57.1kJ/mol  and 13.7Kcal/mol
QUESTION: 19

The heat evolved in the combustion of methane is given by the following equations:

CH4 (g) + 2O2 (g) → CO2 (g) + H2O (l)         ΔH = -890.3 KJ

How many grams of methane would be required to produce 444.15 KJ of heat of combustion:

Solution:

CH4 required = (445.15 x 16) / 890.3 = 8gm

QUESTION: 20

One gram sample of NH4NO3 is decomposed in a bomb calorimeter. The temperature of the calorimeter increases by 6.12 K. The heat capacity of the system is 1.23 kJ/g/deg. What is the molar heat of decomposition for NH4NO3?

Solution:

Heat of decomposition, ΔE = m.s.ΔT
= 1 x 1.23 x 6.12 = 7.5276 kJ
Molar heat of decomposition for NH4NO3 = 7.5276 x 80 = 602.2 kJ/mol

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