M3S6 – Enthalpy Calculations for Year 1

Enthalpy Calculations for Year 1

1 / 10

Using enthalpies of formation Δ_fH, calculate the enthalpy change for the following reaction.

CaCO₃_(s) => CaO_(s) + CO₂_(g)

Select the data from the 'Selection of Enthalpies of Formation and Combustion'.

If this question was generated from Random Retrieval, this data can also be found in TOOLS>Data Sheets.

-777 kJ mol^-1

81.5 kJ mol^-1

178 kJ mol^-1

-178 kJ mol^-1

2 / 10

Using enthalpies of formation Δ_fH, calculate the enthalpy change for the following reaction.

2NaHCO₃_(s) => Na₂CO_3(s) + H₂O_(l) + CO₂_(g)

Select the data from the 'Selection of Enthalpies of Formation and Combustion' shown above.

If this question was generated from Random Retrieval, this data can also be found in TOOLS>Data Sheets.

181.8 kJ mol^-1

45.5 kJ mol^-1

90.9 kJ mol^-1

72.4 kJ mol^-1

3 / 10

Using enthalpies of formation Δ_fH, calculate the enthalpy change for the following hydration process.

Na₂S₂O₃_(s) + 5H₂O_(l) => Na₂S₂O₃•5H₂O_(s)

Select the data from the 'Selection of Enthalpies of Formation and Combustion' shown above.

If this question was generated from Random Retrieval, this data can also be found in TOOLS>Data Sheets.

35 kJ mol^-1

-1199 kJ mol^-1

-5161 kJ mol^-1

-55 kJ mol^-1

4 / 10

Using enthalpies of formation Δ_fH, calculate the enthalpy change for the following esterification reaction.

CH₃COOH_(l) + C₂H₅OH_(l) => CH₃COOCH₂CH₃_(l) + H₂O_(l)

Select the data from the 'Selection of Enthalpies of Formation and Combustion' shown above.

If this question was generated from Random Retrieval, this data can also be found in TOOLS>Data Sheets.

-2 kJ mol^-1

-1 kJ mol^-1

1 kJ mol^-1

4 kJ mol^-1

5 / 10

Using enthalpies of formation Δ_fH, calculate the enthalpy of combustion Δ_cH of ethanol:

C₂H₅OH_(l) + 3O₂_(g) => 2CO₂_(g) + 3H₂O_(l)

Select the data from the 'Selection of Enthalpies of Formation and Combustion' shown above.

If this question was generated from Random Retrieval, this data can also be found in TOOLS>Data Sheets.

-975 kJ mol^-1

-403 kJ mol^-1

-1369 kJ mol^-1

-797 kJ mol^-1

6 / 10

Using enthalpies of combustion Δ_cH, calculate the enthalpy change for the cracking of butane:

C₄H₁₀_(g) => C₂H₆_(g) + C₂H₄_(g)

Select the data from the 'Selection of Enthalpies of Formation and Combustion' shown above.

If this question was generated from Random Retrieval, this data can also be found in TOOLS>Data Sheets.

46.9 kJ mol^-1

93.8 kJ mol^-1

84.5 kJ mol^-1

188 kJ mol^-1

7 / 10

Using enthalpies of combustion Δ_cH, calculate the enthalpy change for the hydrogenation of propene:

C₃H₆_(g) + H_2(g) => C₃H_8(g)

Select the data from theenthalpies of combustion Δ_cH.

If this question was generated from Random Retrieval, this data can also be found in TOOLS>Data Sheets.

-43.9 kJ mol^-1

63.5 kJ mol^-1

-346 kJ mol^-1

-125.1 kJ mol^-1

8 / 10

The enthalpy of combustion Δ_cH of butan-1-ol = -2670 kJ mol^-1

Using this figure and data from the 'Selection of Enthalpies of Formation and Combustion' shown above, calculate the enthalpy of formation Δ_fH of liquid butan-1-ol

A Hess Cycle should be drawn to help you calculate this.

If this question was generated from Random Retrieval, this data can also be found in TOOLS>Data Sheets.

-336 kJ mol^-1

808 kJ mol^-1

846 kJ mol^-1

-569 kJ mol^-1

9 / 10

Using mean bond dissociation enthalpies, estimate the enthalpy of combustion Δ_cH of liquid ethanol

C₂H₅OH_(l) + 3O₂_(g) => 2CO₂_(g) + 3H₂O_(l)

1214 kJ mol^-1

-1274 kJ mol^-1

1725 kJ mol^-1

-1725 kJ mol^-1

10 / 10

The value that you obtain for the enthalpy of combustion Δ_cH of liquid ethanol using mean bond enthalpies is different from the value obtained experimentally, or by using enthalpy of formation Δ_fH of liquid ethanol.

What is the most significant reason for this?

Obtaining the value by experiment allows one to repeat the experiment and take an average.

Mean bond enthalpies can't be used directly to estimate this enthalpy change because ethanol and water are in the liquid state.

Obtaining the value by repeating the experiment allows one to spot anomalous values and then remove them from the calculation of the average.

Use of enthalpies of formation lead to more reliable answers. This is because they have been repeated far more times and the experiments have shown the values to be highly repeatable.

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