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IB Chemistry: Measuring enthalpy changes — Practice Questions & Answers

306 practice questions available for this topic — here are 10 with full answers and explanations.

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Practice questions with answers

1 Multiple choice · Easy

An exothermic reaction is one that:

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WhyAn exothermic reaction releases heat to the surroundings and has a negative enthalpy change ($\Delta H < 0$).
2 Multiple choice · Easy

During an endothermic reaction the temperature of the surroundings:

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WhyAn endothermic reaction absorbs heat from the surroundings, so the temperature of the surroundings falls.
3 Multiple choice · Medium

Which equation is used to calculate the heat energy transferred to or from water in calorimetry?

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WhyThe heat transferred is $q = mc\Delta T$, where $m$ is the mass, $c$ the specific heat capacity and $\Delta T$ the temperature change.
4 Multiple choice · Medium

In what units is an enthalpy change of reaction usually expressed?

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WhyEnthalpy changes of reaction are usually quoted per mole of reaction in $\text{kJ mol}^{-1}$.
5 Multiple choice · Medium

When a fuel is burned under a beaker of water, the heat released by the fuel is assumed to be equal to:

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WhyIn simple calorimetry it is assumed all the heat released by the reaction is absorbed by the water, so heat released $= mc\Delta T$ of the water.
6 Multiple choice · Hard

Burning $0.0100\,\text{mol}$ of a fuel raises the temperature of $100\,\text{g}$ of water by $20.0\,^{\circ}\text{C}$. Using $c = 4.18\,\text{J g}^{-1}\,^{\circ}\text{C}^{-1}$, what is the enthalpy of combustion?

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Why$q = mc\Delta T = 100 \times 4.18 \times 20.0 = 8360\,\text{J} = 8.36\,\text{kJ}$. Per mole: $\Delta H = -8.36/0.0100 = -836\,\text{kJ mol}^{-1}$ (negative, exothermic).
7 Fill in the blank · Easy

The breaking of chemical bonds is an process (it absorbs energy).

Answer: endothermic

WhyBond breaking requires energy input (endothermic), while bond making releases energy (exothermic).
8 Fill in the blank · Medium

Heating $100\,\text{g}$ of water by $5.0\,^{\circ}\text{C}$ ($c = 4.18\,\text{J g}^{-1}\,^{\circ}\text{C}^{-1}$) requires J of heat.

Answer: 2090 / 2090 J / 2.09 / 2.09 kJ

Why$q = mc\Delta T = 100 \times 4.18 \times 5.0 = 2090\,\text{J}$.
9 Multiple choice · Easy

The temperature of a reaction mixture rises as the reaction proceeds. The reaction is

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WhyA temperature rise indicates an exothermic reaction releasing heat to the surroundings.
10 Multiple choice · Medium

In an endothermic reaction, the enthalpy of the products compared with the reactants is

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WhyEndothermic reactions absorb energy, so the products have higher enthalpy than the reactants.

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Practise other IB Chemistry topics

Topic S1.1 (SL/HL): Introduction to the particulate nature of matter Topic S1.2 (SL/HL): The nuclear atom Topic S1.2 (HL): The nuclear atom Topic S1.3 (SL/HL): Electron configurations Topic S1.3 (HL): Electron configurations Topic S1.4 (SL/HL): Counting particles by mass: the mole Topic S1.5 (SL/HL): Ideal gases Topic S2.1 (SL/HL): The ionic model Topic S2.1 (HL): The ionic model Topic S2.2 (SL/HL): The covalent model Topic S2.2 (HL): The covalent model Topic S2.3 (SL/HL): The metallic model Topic S2.3 (HL): The metallic model Topic S2.4 (SL/HL): From models to materials Topic S2.4 (HL): From models to materials Topic S3.1 (SL/HL): The periodic table: classification of elements Topic S3.1 (HL): The periodic table: classification of elements Topic S3.2 (SL/HL): Functional groups: classification of organic compounds Topic S3.2 (HL): Functional groups: classification of organic compounds Topic R1.2 (SL/HL): Energy cycles in reactions Topic R1.2 (HL): Energy cycles in reactions Topic R1.3 (SL/HL): Energy from fuels Topic R1.4 (HL): Entropy and spontaneity Topic R2.1 (SL/HL): How much? The amount of chemical change Topic R2.2 (SL/HL): How fast? The rate of chemical change Topic R2.2 (HL): How fast? The rate of chemical change Topic R2.3 (SL/HL): How far? The extent of chemical change Topic R2.3 (HL): How far? The extent of chemical change Topic R3.1 (SL/HL): Proton transfer reactions Topic R3.1 (HL): Proton transfer reactions Topic R3.2 (SL/HL): Electron transfer reactions Topic R3.2 (HL): Electron transfer reactions Topic R3.3 (SL/HL): Electron sharing reactions Topic R3.4 (SL/HL): Electron-pair sharing reactions Topic R3.4 (HL): Electron-pair sharing reactions