Thermodynamics (A-level only)

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Question 7

Table 1 shows the experimental values of some standard enthalpy changes for sodium bromide, $N a B r$ .

Table 1: Standard Enthalpy Changes

Name of enthalpy change	$mol−1\Delta H^\ominus / \text{kJ mol}^{-1}$
Enthalpy of atomisation of sodium	$+ 107$
First ionisation energy of sodium	$+ 496$
Electron affinity of bromine	$- 325$
Enthalpy of lattice formation of sodium bromide	$- 747$
Enthalpy of formation of sodium bromide	$- 361$

Calculate the standard enthalpy of atomisation of bromine, $ΔHat⊖(Br)\Delta H_{at}^\ominus(\text{Br})$ , using the data in Table 1.

[3]

The experimental value for the enthalpy of lattice formation of sodium bromide is $mol−1-747\text{ kJ mol}^{-1}$ . A theoretical calculation based on the perfect ionic model yields $mol−1-735\text{ kJ mol}^{-1}$ . Deduce what the comparison of these two values indicates about the bonding in sodium bromide.

[2]

Use the standard entropy data in Table 2 to calculate the standard Gibbs free energy change ( $ΔG⊖\Delta G^\ominus$ ) at $K298\text{ K}$ for the decomposition of sodium bromide into its elements:

\rightarrow Na(s) + \frac{1}{2}Br_2(l)

and explain whether this reaction is feasible at $K298\text{ K}$ .

Table 2: Standard Entropies at $K298\text{ K}$

Substance	$mol−1S^\ominus / \text{J K}^{-1}\text{ mol}^{-1}$
$N a B r (s)$	$86.8$
$N a (s)$	$51.3$
$Br_2(l)$	$152.2$

[5]

Thermodynamics (A-level only)

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Question 7

Table 1 shows the experimental values of some standard enthalpy changes for sodium bromide, $N a B r$ .

Table 1: Standard Enthalpy Changes

Name of enthalpy change	$mol−1\Delta H^\ominus / \text{kJ mol}^{-1}$
Enthalpy of atomisation of sodium	$+ 107$
First ionisation energy of sodium	$+ 496$
Electron affinity of bromine	$- 325$
Enthalpy of lattice formation of sodium bromide	$- 747$
Enthalpy of formation of sodium bromide	$- 361$

Calculate the standard enthalpy of atomisation of bromine, $ΔHat⊖(Br)\Delta H_{at}^\ominus(\text{Br})$ , using the data in Table 1.

[3]

[2]

\rightarrow Na(s) + \frac{1}{2}Br_2(l)

and explain whether this reaction is feasible at $K298\text{ K}$ .

Table 2: Standard Entropies at $K298\text{ K}$

Substance	$mol−1S^\ominus / \text{J K}^{-1}\text{ mol}^{-1}$
$N a B r (s)$	$86.8$
$N a (s)$	$51.3$
$Br_2(l)$	$152.2$

[5]

Thermodynamics (A-level only)

Question 7

Table 1: Standard Enthalpy Changes

Table 2: Standard Entropies at $K298\text{ K}$

Markscheme

Thermodynamics (A-level only)

Question 7

Table 1: Standard Enthalpy Changes

Table 2: Standard Entropies at $K298\text{ K}$

Markscheme

Thermodynamics (A-level only)

Question 7

Table 1: Standard Enthalpy Changes

Table 2: Standard Entropies at 298 K298\text{ K}298 K

Thermodynamics (A-level only) Questions

Thermodynamics (A-level only)

Question 7

Table 1: Standard Enthalpy Changes

Table 2: Standard Entropies at 298 K298\text{ K}298 K

Thermodynamics (A-level only) Questions

Table 2: Standard Entropies at $K298\text{ K}$

Table 2: Standard Entropies at $K298\text{ K}$