Thermochemistry MCQs 2026

In a calorimetry experiment, the heat lost by a hot object equals the heat

1. AGained by the surroundings/cooler object (assuming no losses)✓
2. BLost permanently✓
3. CConverted to work only✓
4. DAbsorbed by the container only, not the water✓

Thermochemistry is the branch of chemistry that deals with

1. ARates of chemical reactions✓
2. BStructure of atoms✓
3. CHeat changes accompanying chemical reactions✓
4. DAcid-base titrations✓

A system that can exchange both matter and energy with its surroundings is called

1. AClosed system✓
2. BOpen system✓
3. CIsolated system✓
4. DAdiabatic system✓

A system that can exchange energy but not matter with its surroundings is called

1. AOpen system✓
2. BIsolated system✓
3. CClosed system✓
4. DHomogeneous system✓

An isolated system is one that exchanges

1. ANeither matter nor energy with surroundings✓
2. BOnly matter with surroundings✓
3. COnly energy with surroundings✓
4. DBoth matter and energy freely✓

A reaction that releases heat to the surroundings is called

1. AExothermic✓
2. BEndothermic✓
3. CIsothermal✓
4. DAdiabatic✓

A reaction that absorbs heat from the surroundings is called

1. AExothermic✓
2. BIsothermal✓
3. CIsochoric✓
4. DEndothermic✓

In an exothermic reaction, the enthalpy change (ΔH) is

1. AZero✓
2. BPositive✓
3. CInfinite✓
4. DNegative✓

In an endothermic reaction, the enthalpy change (ΔH) is

1. ANegative✓
2. BPositive✓
3. CZero✓
4. DUndefined✓

The first law of thermodynamics is essentially a statement of the law of conservation of

1. AMass✓
2. BMomentum✓
3. CCharge✓
4. DEnergy✓

According to the first law of thermodynamics, ΔU (change in internal energy) equals

1. Aq - w only when w=0✓
2. Bq + w (heat added plus work done on the system)✓
3. Cw - q✓
4. Dq × w✓

Standard enthalpy of formation refers to the enthalpy change when 1 mole of a compound forms from its elements in their

1. AStandard states✓
2. BMolten states✓
3. CGaseous states only✓
4. DIonic forms✓

The standard enthalpy of formation of an element in its most stable state is defined as

1. AZero✓
2. BOne✓
3. CNegative✓
4. DInfinite✓

Hess's law states that the total enthalpy change of a reaction is

1. ADependent on the reaction pathway✓
2. BAlways zero✓
3. CIndependent of the pathway, depending only on initial and final states✓
4. DOnly valid for exothermic reactions✓

Hess's law is a consequence of which fundamental law

1. ALaw of mass action✓
2. BLe Chatelier's principle✓
3. CLaw of conservation of energy✓
4. DLaw of multiple proportions✓

Calorimetry is the technique used to measure

1. AHeat changes in physical and chemical processes✓
2. BRate of reaction✓
3. CpH of a solution✓
4. DMolar mass of a gas✓

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

1. A1 gram of substance by 1°C✓
2. B1 mole of substance by 100°C✓
3. CThe whole system by 1 K only in gases✓
4. DA given quantity of substance by 1°C (or 1 K)✓

Specific heat capacity is the amount of heat required to raise the temperature of

1. A1 mole of substance by 1 K✓
2. B1 liter of liquid by 1°C✓
3. C1 gram of substance by 1°C✓
4. DThe entire calorimeter by 1°C✓

The specific heat capacity of water is approximately

1. A4.18 J/(g·°C)✓
2. B2.09 J/(g·°C)✓
3. C1.00 J/(g·°C)✓
4. D0.45 J/(g·°C)✓

Bond enthalpy is defined as the energy required to break one mole of a bond in the

1. ALiquid state✓
2. BSolid state✓
3. CAqueous state✓
4. DGaseous state✓

Bond breaking is generally an ___ process, and bond formation is generally an ___ process

1. AExothermic; endothermic✓
2. BEndothermic; exothermic✓
3. CEndothermic; endothermic✓
4. DExothermic; exothermic✓

Enthalpy of combustion refers to the heat released when 1 mole of a substance is completely burned in

1. ANitrogen✓
2. BVacuum✓
3. CWater✓
4. DExcess oxygen✓

Enthalpy of neutralization is the heat released when 1 mole of water is formed from the reaction of

1. ATwo acids✓
2. BTwo bases✓
3. CAn acid and a base✓
4. DA salt and water✓

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. D0 kJ/mol✓

A bomb calorimeter is used to measure the heat of

1. ANeutralization only✓
2. BSolution only✓
3. CFusion✓
4. DCombustion at constant volume✓

Enthalpy of solution is the heat change when 1 mole of a solute

1. AReacts with another solute✓
2. BDissolves completely in a specified amount of solvent✓
3. CEvaporates✓
4. DFreezes✓

Which of the following processes is always endothermic

1. AMelting of a solid✓
2. BFreezing of a liquid✓
3. CCondensation of a gas✓
4. DCombustion of fuel✓

Which of the following processes is always exothermic

1. ACondensation of a vapor into liquid✓
2. BSublimation of a solid✓
3. CMelting of ice✓
4. DVaporization of a liquid✓

The entropy of a system is a measure of its

1. ATotal energy content✓
2. BDegree of disorder or randomness✓
3. CEnthalpy change✓
4. DHeat capacity✓

According to the second law of thermodynamics, the entropy of the universe

1. AAlways decreases✓
2. BRemains constant in all processes✓
3. CIs always zero✓
4. DTends to increase in spontaneous processes✓

Gibbs free energy change (ΔG) determines the ___ of a reaction

1. ARate✓
2. BEnthalpy only✓
3. CSpontaneity✓
4. DMolar mass✓

A reaction is spontaneous at all temperatures when

1. AΔH is negative and ΔS is positive✓
2. BΔH is positive and ΔS is negative✓
3. CΔH is positive and ΔS is zero✓
4. DΔH is negative and ΔS is negative always✓

The relationship between Gibbs free energy, enthalpy, and entropy is given by

1. AΔG = ΔH × TΔS✓
2. BΔG = ΔH / TΔS✓
3. CΔG = ΔH − TΔS✓
4. DΔG = TΔS − ΔH always✓

At equilibrium, the Gibbs free energy change (ΔG) of a reaction is

1. AMaximum✓
2. BNegative and large✓
3. CZero✓
4. DPositive and large✓

The third law of thermodynamics states that the entropy of a perfect crystal at absolute zero is

1. AInfinite✓
2. BNegative✓
3. CMaximum✓
4. DZero✓

Which of the following has the highest entropy under similar conditions

1. AIce (solid)✓
2. BLiquid water✓
3. CA pure crystal✓
4. DWater vapor (gas)✓

The heat of formation of an element in its standard state is by convention taken as

1. APositive✓
2. BNegative✓
3. CZero✓
4. DUndefined✓

For a reaction, ΔH(reaction) can be calculated as

1. ASum of bond enthalpies of products only✓
2. BSum of bond enthalpies broken minus sum of bond enthalpies formed✓
3. CSum of bond enthalpies formed minus bond enthalpies broken✓
4. DAlways zero✓

An adiabatic process is one in which

1. ATemperature remains constant✓
2. BNo heat is exchanged with the surroundings✓
3. CVolume remains constant✓
4. DPressure remains constant✓

An isothermal process is one in which

1. ATemperature remains constant✓
2. BNo heat is exchanged✓
3. CVolume remains constant✓
4. DPressure remains constant✓

An isochoric process occurs at constant

1. APressure✓
2. BVolume✓
3. CTemperature✓
4. DEnthalpy✓

An isobaric process occurs at constant

1. AVolume✓
2. BTemperature✓
3. CEntropy✓
4. DPressure✓

At constant pressure, the heat absorbed or released by a system equals the change in

1. AInternal energy only✓
2. BEntropy✓
3. CGibbs free energy✓
4. DEnthalpy✓

State functions are quantities that depend only on the ___ of the system, not the path taken

1. ARate of reaction✓
2. BInitial and final states✓
3. CCatalyst used✓
4. DContainer shape✓

Which of the following is a state function

1. AHeat (q)✓
2. BWork (w)✓
3. CEnthalpy (H)✓
4. DPath taken during a reaction✓

The enthalpy of a reaction that is the reverse of a known reaction has

1. AThe same sign and magnitude✓
2. BZero value✓
3. CThe same magnitude but opposite sign✓
4. DDouble the magnitude✓

If a reaction is carried out in two steps, the total enthalpy change is

1. AThe average of the two steps✓
2. BThe larger of the two step enthalpies✓
3. CThe sum of enthalpy changes of the two steps (Hess's law)✓
4. DIndependent of the individual steps✓

Lattice enthalpy and enthalpy of hydration together contribute to the overall enthalpy of

1. ASolution✓
2. BNeutralization✓
3. CCombustion✓
4. DFormation✓

A negative enthalpy of solution generally indicates the dissolution process is

1. AEndothermic✓
2. BNon-spontaneous✓
3. CReaction, not dissolution✓
4. DExothermic✓

The unit of enthalpy in the SI system is

1. ACalories only✓
2. BJoules (or kJ/mol)✓
3. CWatts✓
4. DDegrees Kelvin✓