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IBChemistrySLExam QuestionsWhat Drives Chemical Reactions?Measuring Enthalpy Change

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Measuring Enthalpy Change (SL IB Chemistry)

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Measuring Enthalpy Change

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11 mark

Which equation below can represent both an enthalpy change of formation and combustion?

  • CH4(g) + 2O2(g)  →  CO2(g) + 2H2O(l)

  • 2Na(s) + ½O2(g)  →  Na2O(s) 

  • HCl(aq) + NaOH(aq)  →  NaCl(aq) + H2O(l)

  • CO(g) + C(s)  →  CO2(g)

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21 mark

A student carried out an experiment to determine the enthalpy change for the combustion of ethanol.

The following results were obtained by the student. The specific heat capacity of water is 4.18 J g−1 K−1.q1_5-1_ib_sl_easy_mcq

start temperature of the water

21 °C

final temperature of the water

41 °C

mass of alcohol burner before burning

259.75 g

mass of alcohol burner after burning

259.18 g

mass of glass beaker plus water

150.00 g

mass of glass beaker

50.0 g

How much of the heat energy produced by the burning of ethanol went into the water?

  • 8 360 J

  • 12 540 J

  • 47.65 J

  • 17 138 J

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31 mark

When a sample of ammonium chloride is added to a small beaker of water and stirred, the temperature drops as the ammonium chloride slowly dissolves in the water. 

Which statement about the process is true?

  • The process is endothermic and ΔH is -

  • The process is exothermic and ΔH is -

  • The process is endothermic and ΔH is +

  • The process is exothermic and ΔH is +

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41 mark

Which statement is true about all exothermic reactions?

  • Gases are formed during the reaction

  • They give out heat 

  • The reaction is fast

  • They are combustion reactions

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51 mark

Which processes have a negative enthalpy change? 

  1.  The combustion of an alcohol
  2.  The reaction between hydrochloric acid and sodium hydroxide
  3.  Water vapour condensing

  • I and II only  

  • I and III only  

  • II and III only 

  • I, II and III

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61 mark

The enthalpy change of a chemical reaction can be found using the following relationship: 

q = mcΔT 

In this expression, which of the following is true?

  • m represents the amount of substance in moles

  • The temperature is measured in Centigrade

  • c is the specific heat capacity of the substance

  • The unit of q is kJ

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71 mark

Which is the correct definition for the standard enthalpy of combustion?

  • The enthalpy change when the reactants in a stoichiometric equation react to give the products, under standard conditions

  • The enthalpy change when one mole of a substance is burnt in excess oxygen, under standard conditions

  • The enthalpy change when one mole of water is formed by reacting an acid and an alkali, under standard conditions

  • The enthalpy change when one mole of a product is formed from its elements, under standard conditions

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81 mark

1.20 g of ethanol is combusted releasing 35 500 J of energy. 

What is the molar enthalpy change for the combustion of ethanol? 

  • –1 363 kJ mol-1

  • –11 646 kJ mol-1

  • 1 363 kJ mol-1

  • 642 836 kJ mol-1

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91 mark

Which enthalpy change is described as the enthalpy change when the reactants in a stoichiometric equation react, under standard conditions, to form the products?

  • ΔHӨc

  • ΔHӨneut

  • ΔHӨr

  • ΔHӨf

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101 mark

Enthalpy of formation data is often used to calculate the enthalpy of reaction. Which of the following does not have a standard enthalpy of formation of 0 kJ mol-1?

  • C (s)

  • N2 (l)

  • O2 (g)

  • F2 (g)

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111 mark

The reaction pathway for a reversible reaction is shown below:q1_5-3_ib_sl_easy_mcq

Which statement is correct?

  • The activation energy of the reverse reaction is +90 kJ mol–1

  • The activation energy of the forward reaction is +20 kJ mol–1

  • The activation of the reverse reaction is +20 kJ mol–1

  • The enthalpy change of forwards reaction is - 70 kJ mol–1

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121 mark

The reaction pathway for a reversible reaction is shown below.q2_5-3_ib_sl_easy_mcq

Which statements are correct? 

  1. The forward reaction is endothermic.
  2. The enthalpy change for the backward reaction is –30 kJ mol–1.
  3. The activation energy for the forward reaction is +90 kJ mol–1.

  • I and II only 

  • I and III only  

  • II and III only 

  • I, II and III

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131 mark

When a sample of calcium oxide, CaO, is added to dilute hydrochloric acid the temperature rises. Which of the following statements is correct?

  • More bonds are broken than are formed in the reaction

  • More bonds are formed than are broken in the reaction

  • The energy of the bonds broken is greater than of the bonds formed

  • The energy of the bonds broken is less than of the bonds formed

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141 mark

This energy profile diagram represents the reaction pathway for the following reaction:                                   

Y (g) + Z (g) → W (g) + X (g)

q8_5-3_ib_sl_easy_mcq

 Which statement is true about the reverse reaction, W(g) + X(g) → Y(g) + Z(g)?

  • It will have a negative ΔH 

  • It will have a positive ΔH 

  • It will have a smaller activation energy

  • The temperature of the surroundings increase

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151 mark

The reaction of hydrogen with iodine to form hydrogen iodide is shown below: 

H2 + I2 → 2HI 

Use the bond energy data given to calculate the enthalpy of reaction, ΔHӨr.

Bond

Energy, kJ mol-1

H-H

432

I-I

151

H-I

298

  • 881 kJ mol–1

  • 1 179 kJ mol–1

  • –13 kJ mol–1

  • 285 kJ mol–1

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11 mark

A student mixed 30.0 cm3 of 0.0250 mol dm-3 potassium hydroxide solution with 30.0 cm3 of 0.0250 mol dm-3 nitric acid. The temperature rose by 0.50 oC. Assume no heat was lost to the surroundings. 

The mixture had a specific heat capacity of 4.18 J g -1 K-1. 

What is the molar enthalpy change for the reaction?

  • –83 600

  • –167 200 kJ mol–1

  • – 5.98 x 10–6 kJ mol–1

  • –167.2 kJ mol–1

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21 mark

An experiment was carried out to determine the approximate value for the molar enthalpy change of neutralisation. 

75 cm3 of 3.00 mol dm–3 hydrochloric acid was placed in a polystyrene beaker of negligible heat capacity. Its temperature was recorded, and then 75 cm3 of 3.00 mol dm−3 potassium hydroxide at the same temperature was quickly added, and the solution stirred. 

The temperature rose by 14 °C. The resulting solution may be considered to have a specific heat capacity of 4.18 J g-1 K-1. 

What is the value for ΔH?

  • –4 876.7 J mol–1

  • –39 013 J mol–1

  • –39.01 J mol–1

  • –99 972 J mol–1 

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31 mark

The table below discusses three types of enthalpy change:

‘+’ means that this type of standard enthalpy change can only have positive values,

‘–’ means that this type of standard enthalpy change can only have negative values,

‘+ / –’ means that either positive or negative values are possible. 

Which row is correct?

 

formation

combustion

neutralisation

A

+

+

+ / –

B

+ / –

+

+ / –

C

+ / –

–

–

D

–

–

+

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    41 mark

    Using a spirit burner, ethanol is used to heat a container of water.

    In this experiment:

    Mass of ethanol burned, g

    a

    Mass of water, g

    b

    Specific heat capacity of water, J g–1 K–1

    d

    Temperature rise, °C

    y

     

    How much heat energy is absorbed by the water? 

    • ady

    • bdy

    • bd(y+273)

    • (y+273) / ad

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    51 mark

    An iron block with a mass of 0.11 kg absorbs 504 J of heat energy. What is the temperature rise in K?

    Specific heat capacity of iron = 0.448 J g–1 K–1

    • 1.02 x104

    • 1.10

    • 10.23

    • 9.78 x 10-2

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    61 mark

    Which statements are correct for an endothermic reaction? 

    1. The products are more stable than the reactants
    2. The enthalpy change is positive
    3. The temperature of the surroundings decreases

    • I and II only

    • I and III only

    • II and III only 

    • I, II and III

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    71 mark

    Which assumptions are correct when calculating the enthalpy change for a reaction in solution? 

    1. The density of the solution is 1 g cm-3
    2. The specific heat capacity of the solution is 4.18 J g-1 K-1
    3. The correct stoichiometric quantities of reactants for a complete reaction are used 

    • I and II only

    • I and III only

    • II and III only

    • I, II and III

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    81 mark

    What is the closest integer value of the temperature change for this reaction, from the graph

    m1

    • 8

    • 9

    • 11

    • 35

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    91 mark

    Which enthalpy changes correctly describe the following reactions? 

    Reaction 1: HNO3 (aq) + NH3 (aq) → NH4NO3 (aq)

    Reaction 2: CuCO3 (s) → CuO (s) + CO2 (g)

    Reaction 3: S (s) + O2 (g) → SO2 (g)

     

    ΔHӨc

    ΔHӨf

    ΔHӨneut

    ΔHӨr

    A

    2

    2

    1

    3

    B

    3

    2

    1

    2

    C

    3

    3

    1

    2

    D

    2

    3

    1

    3

     

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      101 mark

      Hess’s Law can be used to calculate the enthalpy change for reactions that are difficult to measure experimentally, such as the conversion of graphite to diamond. 

      Which enthalpy data could be used to calculate the enthalpy change for the conversion of graphite to diamond? 

      1. Enthalpy of reaction
      2. Enthalpy of combustion
      3. Enthalpy of formation

      • I and II only

      • I and III only 

      • II and III only 

      • I, II and III

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      111 mark

      Compound R into compound T, it was found that the reaction proceeded by way of compound S, which could be isolated. The following steps were involved. 

      R → S;  ΔH is positive

      S → T; ΔH is negative

      Which reaction profile fits these data?q3_5-3_ib_sl_easy_mcq

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        121 mark

        The reaction pathway for an endothermic reaction is shown.q4_5-3-ib_sl_medium_mcq

         Which arrow represents the activation energy for the reverse reaction?

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          131 mark

          The reaction pathway shows the energies of the reactants, the products and the transition state of a reaction.q5_5-3_ib_sl_medium_mcq

          Which expression correctly represents how to calculate the activation energy of the forward reaction?

          • E3 – E2

          • E2 – E1

          • E2 – E3

          • E1 – E2

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          141 mark

          Four possible reactions (A, B, C and D) of the following equation are measured at the same temperature. 

                                                          X (g) + Y (g) → Z (g) 

          Which reaction pathway diagram shows the reaction occurring rapidly with an overall negative enthalpy value?q8_5-3_ib_sl_medium_mcq

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            151 mark

            Which combination about bond breaking and bond formation energy changes is correct?

             

            Bond breaking

            Bond formation

            A

            endothermic

            endothermic

            B

            endothermic

            exothermic

            C

            exothermic

            endothermic

            D

            exothermic

            exothermic

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              11 mark

              In a calorimetric experiment 2.50 g of a fuel is burnt in oxygen. 30 % of the energy released during the combustion is absorbed by 500 g of water, the temperature of which rises from 25 °C to 68 °C. 

              The specific heat capacity of water is 4.18 J g–1 K–1. 

              What is the total energy released per gram of fuel burnt?

              • 35 948 J

              • 880 587 J

              • 119 827 J 

              • 299 567 J

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              21 mark

              The reaction of hydrochloric acid with sodium hydroxide produced an overall temperature increase of 24.4 K. 

              Given the following data, how much thermal energy was evolved during this reaction? 

              Initial temperature of 25.0 cm3 hydrochloric acid = 17.6 oC

              Initial temperature of 25.0 cm3 sodium hydroxide = 18.5 oC 

              The specific heat capacity of water is 4.18 J g-1 K-1.

              • 1327 J

              • 380 J

              • 209 J

              • 2654 J

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              31 mark

              The temperature rise when 0.1 MJ of heat energy is absorbed by 2.5 kg of solid aluminium is 44.4 oC. 

              What is the specific heat capacity of aluminium, in J g-1 K-1?

              • 901 J g-1 K-1

              • 0.900 J g-1 K-1

              • 9.00 x 10–4 J g-1 K-1

              • 9.00 x 10-6 J g-1 K-1

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              41 mark

              An iron cube, with a mass of 0.5 kg, increases in temperature by 12.7 K when heated. 

              The specific heat capacity of iron is 0.448 J K-1 g-1. 

              What is the enthalpy change, in kJ mol–1, for heating the iron cube?

              • 318 kJ mol–1 

              • 0.318 kJ mol–1

              • -0.318 kJ mol–1 

              • -0.318 kJ mol–1

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              51 mark

              When completing experiments to measure enthalpy change for exothermic processes, which of the following is not a reason for the experimental data to be lower than the expected value?

              • Heat loss through convection

              • Water vapour released as a product

              • An inadequate supply of oxygen during combustion

              • Heat transfer to the system

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              61 mark

              Heptathiepane, S7, can undergo complete combustion to form sulfur dioxide. 

              S7 (s) + 7O2 (g) → 7SO2 (g) 

              Which enthalpy changes can be used to describe this reaction?

               

               

              ΔHfθ

              ΔHcθ

              ΔHr

              A

              ✓

              x

              ✓

              B

              x

              ✓

              ✓

              C

              x

              ✓

              x

              D

              x

              x

              ✓

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                71 mark

                A student obtained the following experimental results for the enthalpy of combustion of cyclohexane (C6H12). 

                Mass of water / g

                50.00

                Initial temperature of the water / °C

                19.60

                Initial mass of spirit burner and cyclohexane / g

                186.79

                Final mass of spirit burner and cyclohexane / g

                186.29

                 

                The student determined from this experiment that the enthalpy of combustion of cyclohexane is –1216 kJ mol–1 

                The specific heat capacity of water = 4.18 J g–1 K–1

                The relative molecular mass (Mr) of cyclohexane = 84.18 

                What is the final temperature of the water in this experiment?

                • 19.63 °C

                • 54.16 °C

                • 999.14 °C

                • 979568.69 °C 

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                81 mark

                The diagrams below show a simple calorimeter that is commonly used in the school laboratory and the more accurate chamber calorimeter.q8_5-1_ib_sl_hard_mcq

                                                               Simple calorimeter

                Chamber calorimeter

                 

                Which of the following statements correctly explain why the chamber calorimeter is more accurate? 

                1. There is less heat loss
                2. There is more complete combustion
                3. There is less fuel lost

                • I and II only 

                • I and III only

                • II and III only 

                • I, II and III

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                91 mark

                Which of the following assumptions are correct when completing the calorimetry experiment and subsequent calculations for the neutralisation of 25.0 cm3 sulfuric acid by 25.0 cm3 barium hydroxide? 

                1. That both solutions have the same initial temperature
                2. The value of m in q = mcΔT is 50 g
                3. Heat is lost to the surroundings

                • I and II only

                • I and III only

                • II and III only

                • I, II and III

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                101 mark

                The heat produced by the combustion of magnesium is used to heat some water. 

                Which values are needed to calculate the energy transferred during the reaction? 

                1. The mass of magnesium
                2. The mass of the water
                3. The temperature change of the water

                • I and II only

                • I and III only

                • II and III only

                • I, II and III

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