The heat capacity of a substance is defined as the heat required to raise the temperature of

A given quantity of substance by 1°C (or 1 K)

The entropy of a system is a measure of its

Degree of disorder or randomness

Thermochemistry MCQs 2026

50 questions with detailed answers · 18 from past papers · 5 quiz batches available

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Page 1 of 1 Questions 1–10 of 50

Q1 medium

The specific heat capacity of water is approximately
1. A 4.18 J/(g·°C)
2. B 2.09 J/(g·°C)
3. C 1.00 J/(g·°C)
4. D 0.45 J/(g·°C)
💡 Explanation:
Water has an unusually high specific heat capacity of about 4.18 joules per gram per degree Celsius.
Q2 Past Paper · PPSC/FPSC/NTS medium

Specific heat capacity is the amount of heat required to raise the temperature of
1. A 1 mole of substance by 1 K
2. B 1 liter of liquid by 1°C
3. C 1 gram of substance by 1°C
4. D The entire calorimeter by 1°C
💡 Explanation:
Specific heat capacity is defined per gram of substance per degree Celsius.
Q3 medium

The heat capacity of a substance is defined as the heat required to raise the temperature of
1. A 1 gram of substance by 1°C
2. B 1 mole of substance by 100°C
3. C The whole system by 1 K only in gases
4. D A given quantity of substance by 1°C (or 1 K)
💡 Explanation:
Heat capacity is the total heat needed to raise a specific quantity of a substance by one degree.
Q4 medium

Which of the following processes is always endothermic
1. A Melting of a solid
2. B Freezing of a liquid
3. C Condensation of a gas
4. D Combustion of fuel
💡 Explanation:
Melting requires energy input to overcome the solid's lattice forces, making it endothermic.
Q5 Past Paper · PPSC/FPSC/NTS medium

The entropy of a system is a measure of its
1. A Total energy content
2. B Degree of disorder or randomness
3. C Enthalpy change
4. D Heat capacity
💡 Explanation:
Entropy quantifies the degree of disorder or randomness within a system.
Q6 medium

According to the second law of thermodynamics, the entropy of the universe
1. A Always decreases
2. B Remains constant in all processes
3. C Is always zero
4. D Tends to increase in spontaneous processes
💡 Explanation:
The second law states that entropy of an isolated system tends to increase over time.
Q7 medium

Gibbs free energy change (ΔG) determines the ___ of a reaction
1. A Rate
2. B Enthalpy only
3. C Spontaneity
4. D Molar mass
💡 Explanation:
A negative ΔG indicates a reaction is thermodynamically spontaneous.
Q8 Past Paper · PPSC/FPSC/NTS medium

A reaction is spontaneous at all temperatures when
1. A ΔH is negative and ΔS is positive
2. B ΔH is positive and ΔS is negative
3. C ΔH is positive and ΔS is zero
4. D ΔH is negative and ΔS is negative always
💡 Explanation:
Negative enthalpy combined with positive entropy makes ΔG negative at every temperature.
Q9 medium

The relationship between Gibbs free energy, enthalpy, and entropy is given by
1. A ΔG = ΔH × TΔS
2. B ΔG = ΔH / TΔS
3. C ΔG = ΔH − TΔS
4. D ΔG = TΔS − ΔH always
💡 Explanation:
The Gibbs-Helmholtz equation defines ΔG as enthalpy minus the product of temperature and entropy.
Q10 medium

At equilibrium, the Gibbs free energy change (ΔG) of a reaction is
1. A Maximum
2. B Negative and large
3. C Zero
4. D Positive and large
💡 Explanation:
At equilibrium, the forward and reverse driving forces balance, making ΔG equal to zero.
Q11 Past Paper · PPSC/FPSC/NTS medium

The third law of thermodynamics states that the entropy of a perfect crystal at absolute zero is
1. A Infinite
2. B Negative
3. C Maximum
4. D Zero
💡 Explanation:
A perfectly ordered crystal at absolute zero has exactly zero entropy according to the third law.
Q12 medium

Which of the following has the highest entropy under similar conditions
1. A Ice (solid)
2. B Liquid water
3. C A pure crystal
4. D Water vapor (gas)
💡 Explanation:
Gas molecules have the most freedom of motion and disorder, giving them the highest entropy.
Q13 medium

The heat of formation of an element in its standard state is by convention taken as
1. A Positive
2. B Negative
3. C Zero
4. D Undefined
💡 Explanation:
Elements in their standard reference states are assigned zero enthalpy of formation by convention.
Q14 Past Paper · PPSC/FPSC/NTS medium

For a reaction, ΔH(reaction) can be calculated as
1. A Sum of bond enthalpies of products only
2. B Sum of bond enthalpies broken minus sum of bond enthalpies formed
3. C Sum of bond enthalpies formed minus bond enthalpies broken
4. D Always zero
💡 Explanation:
Reaction enthalpy equals the energy needed to break bonds minus the energy released forming new bonds.
Q15 medium

Which of the following processes is always exothermic
1. A Condensation of a vapor into liquid
2. B Sublimation of a solid
3. C Melting of ice
4. D Vaporization of a liquid
💡 Explanation:
Condensation releases energy as molecules slow down and form liquid, making it exothermic.
Q16 medium

An adiabatic process is one in which
1. A Temperature remains constant
2. B No heat is exchanged with the surroundings
3. C Volume remains constant
4. D Pressure remains constant
💡 Explanation:
An adiabatic process is defined by zero heat exchange with the surroundings.
Q17 medium

An isothermal process is one in which
1. A Temperature remains constant
2. B No heat is exchanged
3. C Volume remains constant
4. D Pressure remains constant
💡 Explanation:
An isothermal process occurs without any change in temperature.
Q18 Past Paper · PPSC/FPSC/NTS hard

An isochoric process occurs at constant
1. A Pressure
2. B Volume
3. C Temperature
4. D Enthalpy
💡 Explanation:
An isochoric (constant-volume) process keeps the system's volume unchanged.
Q19 hard

An isobaric process occurs at constant
1. A Volume
2. B Temperature
3. C Entropy
4. D Pressure
💡 Explanation:
An isobaric process is defined by constant pressure throughout.
Q20 hard

At constant pressure, the heat absorbed or released by a system equals the change in
1. A Internal energy only
2. B Entropy
3. C Gibbs free energy
4. D Enthalpy
💡 Explanation:
At constant pressure, heat flow directly equals the enthalpy change of the system.
Q21 Past Paper · PPSC/FPSC/NTS hard

State functions are quantities that depend only on the ___ of the system, not the path taken
1. A Rate of reaction
2. B Initial and final states
3. C Catalyst used
4. D Container shape
💡 Explanation:
State functions like enthalpy depend only on initial and final conditions, unlike path-dependent quantities such as heat or work.
Q22 hard

Which of the following is a state function
1. A Heat (q)
2. B Work (w)
3. C Enthalpy (H)
4. D Path taken during a reaction
💡 Explanation:
Enthalpy is a state function, unlike heat and work which depend on the process path.
Q23 hard

The enthalpy of a reaction that is the reverse of a known reaction has
1. A The same sign and magnitude
2. B Zero value
3. C The same magnitude but opposite sign
4. D Double the magnitude
💡 Explanation:
Reversing a reaction inverts the sign of its enthalpy change while keeping the same magnitude.
Q24 Past Paper · PPSC/FPSC/NTS hard

If a reaction is carried out in two steps, the total enthalpy change is
1. A The average of the two steps
2. B The larger of the two step enthalpies
3. C The sum of enthalpy changes of the two steps (Hess's law)
4. D Independent of the individual steps
💡 Explanation:
Hess's law allows total enthalpy change to be found by summing the enthalpies of each step.
Q25 hard

Lattice enthalpy and enthalpy of hydration together contribute to the overall enthalpy of
1. A Solution
2. B Neutralization
3. C Combustion
4. D Formation
💡 Explanation:
Enthalpy of solution results from the balance between lattice energy released and hydration energy absorbed.
Q26 hard

A negative enthalpy of solution generally indicates the dissolution process is
1. A Endothermic
2. B Non-spontaneous
3. C Reaction, not dissolution
4. D Exothermic
💡 Explanation:
A negative enthalpy value means heat is released, characteristic of an exothermic process.
Q27 hard

The unit of enthalpy in the SI system is
1. A Calories only
2. B Joules (or kJ/mol)
3. C Watts
4. D Degrees Kelvin
💡 Explanation:
Enthalpy is measured in joules or kilojoules per mole in the SI system.
Q28 medium

Bond enthalpy is defined as the energy required to break one mole of a bond in the
1. A Liquid state
2. B Solid state
3. C Aqueous state
4. D Gaseous state
💡 Explanation:
Bond enthalpies are conventionally defined for bonds broken in the gaseous phase.
Q29 Past Paper · PPSC/FPSC/NTS medium

Bond breaking is generally an ___ process, and bond formation is generally an ___ process
1. A Exothermic; endothermic
2. B Endothermic; exothermic
3. C Endothermic; endothermic
4. D Exothermic; exothermic
💡 Explanation:
Energy must be absorbed to break bonds, while energy is released when new bonds form.
Q30 medium

Enthalpy of combustion refers to the heat released when 1 mole of a substance is completely burned in
1. A Nitrogen
2. B Vacuum
3. C Water
4. D Excess oxygen
💡 Explanation:
Combustion enthalpy is measured for complete burning of a substance in excess oxygen.
Q31 medium

Enthalpy of neutralization is the heat released when 1 mole of water is formed from the reaction of
1. A Two acids
2. B Two bases
3. C An acid and a base
4. D A salt and water
💡 Explanation:
Neutralization enthalpy corresponds to the heat released forming 1 mole of water from acid and base.
Q32 Past Paper · PPSC/FPSC/NTS medium

The standard enthalpy of neutralization for a strong acid and strong base is approximately
1. A -13.7 kJ/mol
2. B -57.3 kJ/mol
3. C +57.3 kJ/mol
4. D 0 kJ/mol
💡 Explanation:
Strong acid-strong base neutralization consistently releases about 57.3 kJ per mole of water formed.
Q33 medium

A bomb calorimeter is used to measure the heat of
1. A Neutralization only
2. B Solution only
3. C Fusion
4. D Combustion at constant volume
💡 Explanation:
Bomb calorimeters measure combustion heat under constant volume conditions.
Q34 medium

In a calorimetry experiment, the heat lost by a hot object equals the heat
1. A Gained by the surroundings/cooler object (assuming no losses)
2. B Lost permanently
3. C Converted to work only
4. D Absorbed by the container only, not the water
💡 Explanation:
Energy conservation means heat lost by the hotter substance is gained by the cooler surroundings.
Q35 Past Paper · PPSC/FPSC/NTS medium

Enthalpy of solution is the heat change when 1 mole of a solute
1. A Reacts with another solute
2. B Dissolves completely in a specified amount of solvent
3. C Evaporates
4. D Freezes
💡 Explanation:
Enthalpy of solution measures the heat change as a solute fully dissolves in a solvent.
Q36 easy

Thermochemistry is the branch of chemistry that deals with
1. A Rates of chemical reactions
2. B Structure of atoms
3. C Heat changes accompanying chemical reactions
4. D Acid-base titrations
💡 Explanation:
Thermochemistry specifically studies the heat absorbed or released during chemical processes.
Q37 Past Paper · PPSC/FPSC/NTS easy

A system that can exchange both matter and energy with its surroundings is called
1. A Closed system
2. B Open system
3. C Isolated system
4. D Adiabatic system
💡 Explanation:
An open system freely exchanges both matter and energy with its surroundings.
Q38 Past Paper · PPSC/FPSC/NTS easy

A system that can exchange energy but not matter with its surroundings is called
1. A Open system
2. B Isolated system
3. C Closed system
4. D Homogeneous system
💡 Explanation:
A closed system allows energy transfer but keeps matter contained within its boundary.
Q39 easy

An isolated system is one that exchanges
1. A Neither matter nor energy with surroundings
2. B Only matter with surroundings
3. C Only energy with surroundings
4. D Both matter and energy freely
💡 Explanation:
An isolated system is completely sealed off, exchanging neither matter nor energy.
Q40 Past Paper · PPSC/FPSC/NTS easy

A reaction that releases heat to the surroundings is called
1. A Exothermic
2. B Endothermic
3. C Isothermal
4. D Adiabatic
💡 Explanation:
Exothermic reactions release heat energy to their surroundings.
Q41 easy

A reaction that absorbs heat from the surroundings is called
1. A Exothermic
2. B Isothermal
3. C Isochoric
4. D Endothermic
💡 Explanation:
Endothermic reactions absorb heat energy from their surroundings.
Q42 Past Paper · PPSC/FPSC/NTS easy

In an exothermic reaction, the enthalpy change (ΔH) is
1. A Zero
2. B Positive
3. C Infinite
4. D Negative
💡 Explanation:
Exothermic reactions release energy, giving them a negative enthalpy change by convention.
Q43 easy

In an endothermic reaction, the enthalpy change (ΔH) is
1. A Negative
2. B Positive
3. C Zero
4. D Undefined
💡 Explanation:
Endothermic reactions absorb energy, giving them a positive enthalpy change.
Q44 Past Paper · PPSC/FPSC/NTS easy

The first law of thermodynamics is essentially a statement of the law of conservation of
1. A Mass
2. B Momentum
3. C Charge
4. D Energy
💡 Explanation:
The first law states energy can neither be created nor destroyed, only transformed.
Q45 easy

According to the first law of thermodynamics, ΔU (change in internal energy) equals
1. A q - w only when w=0
2. B q + w (heat added plus work done on the system)
3. C w - q
4. D q × w
💡 Explanation:
The first law is expressed as ΔU = q + w, combining heat and work done on the system.
Q46 medium

Standard enthalpy of formation refers to the enthalpy change when 1 mole of a compound forms from its elements in their
1. A Standard states
2. B Molten states
3. C Gaseous states only
4. D Ionic forms
💡 Explanation:
Standard formation enthalpy uses elements in their most stable standard states at given conditions.
Q47 Past Paper · PPSC/FPSC/NTS medium

The standard enthalpy of formation of an element in its most stable state is defined as
1. A Zero
2. B One
3. C Negative
4. D Infinite
💡 Explanation:
By convention, elements in their standard reference state have zero enthalpy of formation.
Q48 medium

Hess's law states that the total enthalpy change of a reaction is
1. A Dependent on the reaction pathway
2. B Always zero
3. C Independent of the pathway, depending only on initial and final states
4. D Only valid for exothermic reactions
💡 Explanation:
Hess's law states enthalpy change depends only on initial and final states, not the path taken.
Q49 Past Paper · PPSC/FPSC/NTS medium

Hess's law is a consequence of which fundamental law
1. A Law of mass action
2. B Le Chatelier's principle
3. C Law of conservation of energy
4. D Law of multiple proportions
💡 Explanation:
Since enthalpy is a state function, Hess's law follows directly from energy conservation.
Q50 medium

Calorimetry is the technique used to measure
1. A Heat changes in physical and chemical processes
2. B Rate of reaction
3. C pH of a solution
4. D Molar mass of a gas
💡 Explanation:
Calorimetry experimentally measures the heat absorbed or released during a process.

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