Structure 1. Models of the particulate nature of matter

1.1 Introduction to the particulate nature of matter

1.2 The nuclear atom

1.3 Electron configurations

1.4 The mole

1.5 Ideal gases

Structure 2. Models of bonding and structure

2.1 The ionic model

2.2 The covalent model

2.3 The metallic model

2.4 From models to materials

Structure 3. Classification of matter

3.1 The periodic table

3.2 Functional groups: Organic compounds

Reactivity 1. What drives chemical reactions?

1.1 Measuring enthalpy changes

1.2 Energy cycles

1.3 Energy from fuels

Reactivity 2. How much, how fast and how far?

2.1 Amount of chemical change

2.2 Rate of chemical change

2.3 Extent of chemical change

Reactivity 3. What are the mechanisms of chemical change?

3.1 Proton transfer reactions

3.2 Electron transfer reactions

3.3 Electron sharing reactions (Radicals)

3.4 Electron-pair sharing reactions

IB Chemistry SL 1.1 Measuring enthalpy changes Question Bank

[Maximum number: 4]

A student carried out an experiment to determine the concentration of a hydrochloric acid solution and the enthalpy change of the reaction between aqueous sodium hydroxide and this acid by thermometric titration.

She added $5.0 \mathrm{~cm}^{3}$ portions of hydrochloric acid to $25.0 \mathrm{~cm}^{3}$ of $1.00 \mathrm{moldm}^{-3}$ sodium hydroxide solution in a glass beaker until the total volume of acid added was $50.0 \mathrm{~cm}^{3}$ , measuring the temperature of the mixture each time. Her results are plotted in the graph below.

The initial temperature of both solutions was the same.

(a)

(i)

Determine the change in temperature, $\Delta T$ .

[ 1 ]

(ii)

Calculate the enthalpy change, in $\mathrm{kJ} \mathrm{mol}^{-1}$ , for the reaction of hydrochloric acid and sodium hydroxide solution.

[ 3 ]

(a)

Magnesium sulfate can exist in either the hydrated form or in the anhydrous form. Two students wished to determine the enthalpy of hydration of anhydrous magnesium sulfate. They measured the initial and the highest temperature reached when anhydrous magnesium sulfate, $\mathrm{MgSO}_{4}(\mathrm{~s})$ , was dissolved in water. They presented their results in the following table.

[ 2 ]

(i)

Calculate the enthalpy change, $\Delta H_{1}$ , for anhydrous magnesium sulfate dissolving in water, in $\mathrm{kJ} \mathrm{mol}^{-1}$ . State your answer to the correct number of significant figures.

[ 2 ]

[Maximum number: 1]

Ethane-1,2-diol, $\mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{OH}$ , has a wide variety of uses including the removal of ice from aircraft and heat transfer in a solar cell.

(a)

Ethane-1,2-diol can be formed according to the following reaction.

2 \mathrm{CO}(\mathrm{~g})+3 \mathrm{H}_{2}(\mathrm{~g}) \rightleftharpoons \mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{OH}(\mathrm{~g})

[ 1 ]

(i)

The enthalpy change, $\Delta H^{\ominus}$ , for the following similar reaction is -233.8 kJ .

2 \mathrm{CO}(\mathrm{~g})+3 \mathrm{H}_{2}(\mathrm{~g}) \rightleftharpoons \mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{OH}(\mathrm{l})

Deduce why this value differs from your answer to (a)(iii).

[ 1 ]

[Maximum number: 4]

A student titrated an ethanoic acid solution, $\mathrm{CH}_{3} \mathrm{COOH}(\mathrm{aq})$ , against $50.0 \mathrm{~cm}^{3}$ of $0.995 \mathrm{~mol} \mathrm{dm}^{-3}$ sodium hydroxide, NaOH(aq), to determine its concentration.
The temperature of the reaction mixture was measured after each acid addition and plotted against the volume of acid.

(a)

(i)

Determine the heat change, q, in kJ , for the neutralization reaction between ethanoic acid and sodium hydroxide.
Assume the specific heat capacities of the solutions and their densities are those of water.

[ 2 ]

(ii)

Calculate the enthalpy change, $\Delta H$ , in $\mathrm{kJ} \mathrm{mol}^{-1}$ , for the reaction between ethanoic acid and sodium hydroxide.

[ 2 ]

[Maximum number: 3]

3.26 g of iron powder are added to $80.0 \mathrm{~cm}^{3}$ of $0.200 \mathrm{~mol} \mathrm{dm}^{-3}$ copper(II) sulfate solution. The following reaction occurs:

\mathrm{Fe}(\mathrm{~s})+\mathrm{CuSO}_{4}(\mathrm{aq}) \rightarrow \mathrm{FeSO}_{4}(\mathrm{aq})+\mathrm{Cu}(\mathrm{~s})

(a)

(i)

The reaction was carried out in a calorimeter. The maximum temperature rise of the solution was $7.5^{\circ} \mathrm{C}$ .

Calculate the enthalpy change, $\Delta H$ , of the reaction, in kJ , assuming that all the heat released was absorbed by the solution. Use sections 1 and 2 of the data booklet.

[ 2 ]

(ii)

State another assumption you made in (b)(i).

[ 1 ]

[Maximum number: 1]

Ammonium nitrate, $\mathrm{NH}_{4} \mathrm{NO}_{3}$ , is used as a high nitrogen fertilizer.

(a)

Cold packs contain ammonium nitrate and water separated by a membrane.

[ 1 ]

(i)

The mass of the contents of the cold pack is 25.32 g and its initial temperature is $25.2^{\circ} \mathrm{C}$ . Once the contents are mixed, the temperature drops to $0.8^{\circ} \mathrm{C}$ .

Calculate the energy, in J , absorbed by the dissolution of ammonium nitrate in water within the cold pack. Assume the specific heat capacity of the solution is $4.18 \mathrm{~J} \mathrm{~g}^{-1} \mathrm{~K}^{-1}$ . Use section 1 of the data booklet.

[ 1 ]

[Maximum number: 1]

Ethyne, $\mathrm{C}_{2} \mathrm{H}_{2}$ , reacts with oxygen in welding torches.

(a)

Ethyne reacts with steam.

Two possible products are:

[ 1 ]

(i)

The enthalpy change for the reaction to produce B is -213 kJ .

Predict, giving a reason, which product is the most stable.

[ 1 ]

[Maximum number: 1]

Two groups of students (Group A and Group B) carried out a project* on the chemistry of some group 7 elements (the halogens) and their compounds.

(a)

In the first part of the project, the two groups had a sample of iodine monochloride (a corrosive brown liquid) prepared for them by their teacher using the following reaction.

\mathrm{I}_{2}(\mathrm{~s})+\mathrm{Cl}_{2}(\mathrm{~g}) \rightarrow 2 \mathrm{ICl}(\mathrm{l})

The following data were recorded.

[ 1 ]

(i)

Using a digital thermometer, the students discovered that the reaction was exothermic. State the sign of the enthalpy change of the reaction, $\Delta H$ .

[ 1 ]

[Maximum number: 2]

Lithium reacts with water to form an alkaline solution.

(a)

Describe two observations that indicate the reaction of lithium with water is exothermic.

[ 2 ]

[Maximum number: 4]

A student was asked to identify an unknown metal with a mass of 1.28 g using calorimetry. The metal was placed in beaker A with boiling water at $100.00^{\circ} \mathrm{C}$ until the metal reached the same temperature as the water. The metal was then quickly transferred to beaker B with 5.65 g of water which had an initial temperature of $25.00^{\circ} \mathrm{C}$ . The final temperature of the water in beaker B and the metal was $26.77^{\circ} \mathrm{C}$ .

(a)

Determine the amount of energy transferred from the metal to the water in beaker B using sections 1 and 2 of the data booklet.

[ 2 ]

(b)

Determine the specific heat capacity of the metal assuming the heat absorbed by the water in beaker B in (a) is equal to the heat released by the metal.

Use section 1 of the data booklet.

If you did not get an answer to (a) use 40.5 J although this is not the correct answer.

[ 2 ]

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