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Edexcel IAL Chemistry 6.5 Calorimetry calculations

Find the temperature change and heated mass, apply q=mcΔT in joules, convert to kilojoules and divide by reacting moles before assigning the enthalpy sign.

Syllabus
First assessment 2019
Course
Chemistry YCH11
Level
AS

Exam points

  • Apply q=mcΔT with solution mass, heat capacity and temperature change in correct units.
  • Convert heat transferred into molar enthalpy with the correct sign and units.
  • Rearrange calorimetry relationships to find missing mass, amount or temperature.

6.5—Experimental data to calculate: i energy transferred in a reaction recalling and using the expression: energy transferred question 1

[Maximum number: 7]

Fuels

Fuels burn in oxygen to release a lot of energy.
Many hydrocarbons and alcohols are used as fuels. During complete combustion, they produce carbon dioxide and water.

Petrol contains 2,2,4-trimethylpentane, an isomer of octane, that promotes smooth combustion.

Figure for Question 6.5—Experimental data to calculate: i energy transferred in a reaction recalling and using the expression: energy transferred question 1 — Edexcel A-Level Chemistry AS

2,2,4-trimethylpentane

Alcohols, such as methanol and ethanol, can be used as fuels either on their own or as additives in petrol.

Question (a)

(a)

The standard enthalpy change of combustion, ΔcH⊖\Delta_{\mathrm{c}} H^{\ominus}, of 2,2,4-trimethylpentane is −5461 kJ mol−1-5461 \mathrm{~kJ} \mathrm{~mol}^{-1}.

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Question (i)

(i)

Calculate the heat energy released during the complete combustion of 1dm31 \mathrm{dm}^{3} of 2,2,4-trimethylpentane.
[Density of 2,2,4-trimethylpentane =0.692 g cm−3=0.692 \mathrm{~g} \mathrm{~cm}^{-3} ]

[ 3 ]

Question (b)

(b)

In an experiment to determine the enthalpy change of combustion of ethanol, C2H5OH\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}, a student used the apparatus shown.

Figure for Question (b) — Edexcel A-Level Chemistry AS

Results:
Mass of water =100.0 g=100.0 \mathrm{~g}
Mass of ethanol used =0.305 g=0.305 \mathrm{~g}
Temperature rise of water =13.2∘C=13.2^{\circ} \mathrm{C}

[ 4 ]

Question (i)

(i)

Calculate the enthalpy change of combustion of ethanol.

Give your answer to an appropriate number of significant figures, and include a sign and units.
[Specific heat capacity of water =4.18 J g−1C−1=4.18 \mathrm{~J} \mathrm{~g}^{-1} \mathrm{C}^{-1} ]

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