A student experimentally determined the molar enthalpy of combustion of ethanol (M = 46.0 g mol−1) using the equipment shown in the following simplified diagram. The student made the following experimental measurements. Mass of water in beaker = 100.0 g Amount of ethanol combusted = 0.0200 mol Temperature rise of the water = 40.0 °C The molar enthalpy of combustion of ethanol calculated from the student’s results is A. -167. kJ mol−1 B. -182. kJ mol−1 C. -334 kJ mol−1 D. -336 kJ mol−1

SSCE VCE Chemistry Measuring Changes in Chemical Reactions: A student experimentally determi

A student experimentally determined the molar enthalpy of combustion of ethanol (M = 46.0 g mol−1) using the equipment shown in the following simplified diagram - VCE - SSCE Chemistry - Question 9 - 2011 - Paper 1

Question 9

A student experimentally determined the molar enthalpy of combustion of ethanol (M = 46.0 g mol−1) using the equipment shown in the following simplified diagram. Th... show full transcript

Worked Solution & Example Answer:A student experimentally determined the molar enthalpy of combustion of ethanol (M = 46.0 g mol−1) using the equipment shown in the following simplified diagram - VCE - SSCE Chemistry - Question 9 - 2011 - Paper 1

Step 1

Calculate the heat absorbed by water (q)

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Answer

To find the heat absorbed by the water, we use the formula:

$q = m \cdot c \cdot \Delta T$

where:

m = mass of water = 100.0 g = 0.100 kg
c = specific heat capacity of water = 4.18 kJ/kg·°C
(\Delta T = 40.0 °C)

Substituting the values:

$q = 0.100 \: \text{kg} \cdot 4.18 \: \text{kJ/kg·°C} \cdot 40.0\: °C = 16.72 \: \text{kJ}$

Step 2

Calculate the molar enthalpy of combustion (ΔH)

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Answer

The molar enthalpy of combustion (ΔH) is calculated using the formula:

$\Delta H = \frac{q}{n}$

where:

q = heat absorbed by water = 16.72 kJ
n = amount of ethanol combusted = 0.0200 mol

Substituting the values:

$\Delta H = \frac{16.72 \: \text{kJ}}{0.0200 \: \text{mol}} = 836.0 \: \text{kJ/mol}$

Since this is a combustion reaction, it is exothermic, and the value should be reported as negative:

$\Delta H = -836.0 \: \text{kJ/mol}$

Step 3

Select the correct answer from the options

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Answer

Based on the calculation, the molar enthalpy of combustion is -836 kJ mol−1. Therefore, the correct option is:

D. -336 kJ mol−1

A student experimentally determined the molar enthalpy of combustion of ethanol (M = 46.0 g mol−1) using the equipment shown in the following simplified diagram - VCE - SSCE Chemistry - Question 9 - 2011 - Paper 1

Worked Solution & Example Answer:A student experimentally determined the molar enthalpy of combustion of ethanol (M = 46.0 g mol−1) using the equipment shown in the following simplified diagram - VCE - SSCE Chemistry - Question 9 - 2011 - Paper 1

Calculate the heat absorbed by water (q)

Calculate the molar enthalpy of combustion (ΔH)

Select the correct answer from the options

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