Thermochemistry MCQs with Answers
Which of the following processes is exothermic?
Melting ice
Boiling water
Dissolving ammonium chloride in water
Combustion of carbon
In an endothermic reaction, heat is:
Released to the surroundings
Neither absorbed nor released
First released, then absorbed
Absorbed from the surroundings
Which of the following is an example of a spontaneous process?
Pumping water uphill
Transfer of heat from a cold to a hot reservoir
Formation of nitric oxide from nitrogen and oxygen at ordinary conditions
Neutralization of a strong acid with a strong base
A non-spontaneous process is characterized by:
Occurring without external assistance
Moving from equilibrium to non-equilibrium
Being unidirectional
Requiring continuous external energy input
Which of the following statements is true about spontaneous processes?
All exothermic reactions are spontaneous.
All endothermic reactions are non-spontaneous.
Spontaneous processes always lead to a decrease in energy
Spontaneous processes proceed towards equilibrium.
What is a 'system' in thermochemistry?
The surroundings of a reaction
The boundary separating reactants and products
The universe
Anything under test or consideration
Which of the following is NOT a state function?
Pressure
Volume
Internal Energy
Heat
A state function is a property that:
Depends on the path taken to reach a state
Is constantly changing
Is irrelevant to thermodynamics
Has definite values for initial and final states
The total energy of a system is called:
Enthalpy
Kinetic Energy
Potential Energy
Internal Energy
According to the first law of thermodynamics:
Energy can be created but not destroyed
Energy can be destroyed but not created
The total energy of the universe is decreasing
Energy can neither be created nor destroyed
Internal energy (E) change is equal to
Heat (q) - Work (w)
Heat (q) / Work (w)
Heat (q) * Work (w)
Heat (q) + Work (w)
In the equation ΔE = q - PΔV, what does PΔV represent?
Change in internal energy
Heat absorbed by the system
Change in enthalpy
Pressure-volume work
When the volume of a gas is kept constant, the change in internal energy is equal to:
Pressure
Work done
Enthalpy change
Heat absorbed at constant volume
Enthalpy (H) is defined as:
Which of the following is true for enthalpy?
It is a path function.
It can be measured absolutely.
It is not related to internal energy.
It is a state function.
In an exothermic reaction
ΔH is positive
ΔH is zero
Temperature decreases
ΔH is negative
Which of the following reactions is endothermic based on the information provided?
Combustion of carbon
Formation of water from hydrogen and oxygen
Haber's process (formation of ammonia)
Formation of nitrogen oxide from nitrogen and oxygen
What happens to the temperature of the system during an exothermic reaction?
It decreases
It remains constant
It fluctuates
It increases
Which of the following factors determines the spontaneity of a reaction, according to the text?
Only the energy change
Only the enthalpy change
Only the entropy change
Free energy of the system
What are the units in which heat changes are usually expressed in the SI system?
A process that proceeds on its own without external assistance is termed as:
Endothermic
Exothermic
Non-spontaneous
Spontaneous
Which of the following is a characteristic of a spontaneous process?
It is reversible.
It requires continuous energy input
It moves from equilibrium to non-equilibrium.
It is irreversible.
In a spontaneous process, systems move towards:
Higher energy states
Non-equilibrium states
Lower entropy states
Equilibrium states
A non-spontaneous process requires:
No energy input
Decrease in entropy
Increase in enthalpy
Continuous energy input
Which of the following is an example of a non-spontaneous process?
Rusting of iron
Dissolving sugar in water
Melting of ice at room temperature
Pumping water uphill
What is the term for the part of the universe under study?
Surroundings
Boundary
State
System
The portion of the universe outside the system is known as:
Boundary
State function
Equilibrium
Surroundings
The real or imaginary surface separating the system from the surroundings is called the:
Interface
State
Function
Boundary
Which of the following is a state function?
State functions depend on:
The path taken to reach a state
The rate of the process
External conditions
Initial and final states only
The sum of kinetic and potential energies of a system is called:
Enthalpy
Work
Heat capacity
Internal energy
Which of the following is NOT a way to transfer energy to or from a system?
Heat
Work
Radiation
Pressure
According to the first law of thermodynamics, energy:
Can be created
Can be destroyed
Always increases
Is always conserved
What does 'q' represent in thermodynamic equations?
Work done
Volume change
Pressure change
Heat transferred
In the context of pressure-volume work, when work is done by the system, the sign of W is:
Positive
Zero
Constant
Negative
If the volume of a gas is not allowed to change, then ΔV equals:
1
Infinity
A constant value
0
Enthalpy is defined mathematically as:
H = E - PV
H = q - w
H = q + w
H = E + PV
What is measured during a change in the state of a system?
Absolute enthalpy
Absolute internal energy
Total energy
Change in enthalpy (ΔH)
For a reaction at constant atmospheric pressure, heat is used:
Only increase internal energy
Only do work on the surroundings
Decrease internal energy
Increase internal energy and do work on the surroundings
What is the term for heat content?
Internal energy
Work
Entropy
Enthalpy
At constant pressure, the heat exchanged by a system with its surroundings is called:
Internal energy
Work done
Free energy
Enthalpy change
Which mathematical expression defines enthalpy (H)?
H = E - PV
H = q + W
H = q - W
H = E + PV
For a reaction that occurs at constant pressure, the change in enthalpy (ΔH) is equal to:
ΔE - PΔV
qv (heat at constant volume)
w (work done)
ΔE + PΔV
Which of the following is true regarding enthalpy?
It can be measured directly.
It is not a state function.
It is path-dependent.
Only the change in enthalpy can be measured.
In an exothermic reaction, the enthalpy change (ΔH) is:
Positive
Zero
Unpredictable
Negative
In an endothermic reaction, the enthalpy change (ΔH) is:
Negative
Zero
Constant
Positive
Which of the following is an example of an exothermic reaction?
Melting ice
Boiling water
Evaporation of alcohol
Combustion of fuel
Which of the following is an example of an endothermic reaction?
Burning of methane gas
Neutralization of acid with a base
Rusting of iron
Dissolving ammonium chloride in water
The amount of heat evolved during the combustion of carbon in oxygen is -393.7 kJ/mol. This reaction is:
Endothermic
Neither endothermic nor exothermic
Cannot be determined
Exothermic
What quantity of heat is absorbed when one mole of nitrogen combines with one mole of oxygen to yield nitrogen oxide (NO)?
-180.51 kJ
-41.6 kJ
+41.6 kJ
+180.51 kJ
The first law of thermodynamics is also known as the:
Law of entropy
Law of enthalpy
Law of heat exchange
Law of conservation of energy
What does the symbol 'w' represent in thermodynamics?
If a system absorbs heat from the surroundings, the value of 'q' is:
Negative
Zero
Constant
Positive
If a system does work on the surroundings, the value of 'w' is:
Positive
Zero
Variable
Negative
A process is spontaneous if it:
Requires continuous external energy
Moves towards a non-equilibrium state
Decreases entropy
Occurs on its own
Which of the following processes is non-spontaneous?
Rusting of iron
Evaporation of water at room temperature
Dissolving salt in water
Flow of heat from cold to hot reservoir
A state function is a property that depends on:
The path taken
Rate of the process
External conditions
Initial and final states
Which of the following is NOT a state function?
Internal Energy
Enthalpy
Volume
Heat
The surface separating the system from the surroundings is called the:
Interface
State
Function
Boundary
In the equation ΔE = q - PΔV, if ΔV = 0, then ΔE is equal to:
In a system, 500 J of heat is absorbed and 200 J of work is done by the system. What is the change in internal energy?
If a reaction occurs in a closed container and the internal energy increases by 300 J while 100 J of work is done on the system, how much heat was transferred?
For a reaction at constant pressure, the change in internal energy is 200 kJ, and the system does 50 kJ of work. What is the enthalpy change?
A gas expands against a constant external pressure of 2 atm, and its volume increases from 10 L to 15 L. If the internal energy change is 400 J, what is the enthalpy change? (1 L atm = 101.3 J)
A system releases 400 J of heat and has 100 J of work done on it. Calculate the change in internal energy.
If a reaction absorbs 250 J of heat and the system expands, performing 100 J of work, what is the change in internal energy (ΔE)?
Thermochemical data can provide insight into the:
Rate of a reaction only
Equilibrium constant only
Color of reactants
Strength of chemical bonds
Which of the following is NOT directly determined by thermochemical measurements?
Bond energies
Reaction spontaneity
Enthalpy change
Reaction rate
A reaction has a negative enthalpy change (ΔH) and occurs spontaneously at room temperature. What can be inferred?
The reaction is endothermic.
The reaction rate is fast.
The reaction is non-spontaneous at high temperatures.
The reaction favors product formation
Consider the formation of a chemical bond. Thermochemical principles suggest that this process is typically:
Exothermic and decreases stability
Endothermic and increases stability
Endothermic and decreases stability
Exothermic and increases stability
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