The table shows the formula, state, and standard molar entropies of the first five straight-chain alkanes. Alkane CH 4 g C 2 H 6 g C 3 H 8 g C 4 H 10 g C 5 H 12 l ∆ S ⊝ J K - 1 mol - 1 186 . 2 229 . 5 269 . 9 310 . 1 261 . 2 Describe and explain the trend in the standard molar entropies of these alkanes.

The standard molar entropies of given alkanes: The entropy of a system is increase whenever its particles have more freedom of motion. Thus, the entropy increases whenever you have more moles of gaseous products than of reactants and whenever you have more product particles in solution than you have of reactant particles. Simpler substances with fewer atoms have lower entropy values than more complex substances and with a greater number of atoms. Hence, the butane has higher entropy than the remaining members, but pentane has lesser entropy than the butane because pentane is a liquid. Gases have higher entropy than liquids.

The table shows the formula, state, and standard molar entropies of the first five straight-chain alkanes. Alkane CH 4 g C 2 H 6 g C 3 H 8 g C 4 H 10 g C 5 H 12 l ∆ S ⊝ J K - 1 mol - 1 186 . 2 229 . 5 269 . 9 310 . 1 261 . 2 Estimate the value of the standard molar entropy of the straight-chain alkane with the formula.

Given: Here is the chemical reaction: C 6 H 14 l → CH 4 g + C 5 H 12 l So, the standard molar entropy of the hexane is = 261 . 2 + 186 . 2 = 447 . 4 J K - 1 mol - 1 .

EASY

AS and A Level

IMPORTANT

Earn 100

When ethanol undergoes combustion, carbon dioxide and water are formed.

$C_{2} H_{5} OH (l) + 3 O_{2} (g) \to 2 {CO}_{2} (g) + 3 H_{2} O (l)$ .

Calculate the standard entropy change for this reaction.

Values for

$S^{⊝} in J K^{- 1} {mol}^{- 1}; C_{2} H_{5} OH (l) = 160.7, O_{2} (g) = 205.0, {CO}_{2} (g) = 213.6, H_{2} O (l) = 69.90 .$

Important Questions on Entropy and Gibbs Free Energy

EASY

AS and A Level

IMPORTANT

Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 23 - Entropy and Gibbs Free Energy>EXAM-STYLE QUESTIONS>Q 2

Calculate the Gibbs free change for the given reaction.

When ethanol undergoes combustion, carbon dioxide and water are formed.

$C_{2} H_{5} OH (l) + 3 O_{2} (g) \to 2 {CO}_{2} (g) + 3 H_{2} O (l)$ .

Values for

$∆ G_{f}^{⊝} in kJ {mol}^{- 1} : C_{2} H_{5} OH (l) = - 174.9, O_{2} (g) = 0, {CO}_{2} (g) = - 394.4, H_{2} O (l) = - 237.2 .$

EASY

AS and A Level

IMPORTANT

Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 23 - Entropy and Gibbs Free Energy>EXAM-STYLE QUESTIONS>Q 2

Calculate the enthalpy change at $298 K$ . Given:

$∆ G_{reaction}^{⊝} = - 1325.5 kJ {mol}^{- 1} ∆ S_{system}^{⊝} = - 138.8 J K^{- 1} {mol}^{- 1} .$

EASY

AS and A Level

IMPORTANT

Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 23 - Entropy and Gibbs Free Energy>EXAM-STYLE QUESTIONS>Q 5

For the following reaction, state whether the entropy of the system decreases or increases. Explain your answer in terms of the order or disorder of the particles.

$NaCl (s) + aq \to {Na}^{+} (aq) + {Cl}^{-} (aq)$ .

EASY

AS and A Level

IMPORTANT

Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 23 - Entropy and Gibbs Free Energy>EXAM-STYLE QUESTIONS>Q 5

For the following reaction: State whether the entropy of the system decreases or increases. Explain your answer in terms of the order or disorder of the particles.

H_{2} O (g) \to H_{2} O (l)

EASY

AS and A Level

IMPORTANT

Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 23 - Entropy and Gibbs Free Energy>EXAM-STYLE QUESTIONS>Q 5

The table shows the formula, state, and standard molar entropies of the first five straight-chain alkanes.

Alkane	${CH}_{4} (g)$	$C_{2} H_{6} (g)$	$C_{3} H_{8} (g)$	$C_{4} H_{10} (g)$	$C_{5} H_{12} (l)$
$\frac{∆ S^{⊝}}{J K^{- 1} {mol}^{- 1}}$	$186.2$	$229.5$	$269.9$	$310.1$	$261.2$

Describe and explain the trend in the standard molar entropies of these alkanes.

EASY

AS and A Level

IMPORTANT

Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 23 - Entropy and Gibbs Free Energy>EXAM-STYLE QUESTIONS>Q 5

The table shows the formula, state, and standard molar entropies of the first five straight-chain alkanes.

Alkane	${CH}_{4} (g)$	$C_{2} H_{6} (g)$	$C_{3} H_{8} (g)$	$C_{4} H_{10} (g)$	$C_{5} H_{12} (l)$
$\frac{∆ S^{⊝}}{J K^{- 1} {mol}^{- 1}}$	$186.2$	$229.5$	$269.9$	$310.1$	$261.2$

Estimate the value of the standard molar entropy of the straight-chain alkane with the formula.

EASY

AS and A Level

IMPORTANT

Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 23 - Entropy and Gibbs Free Energy>EXAM-STYLE QUESTIONS>Q 6

Define standard free energy change of formation.

EASY

AS and A Level

IMPORTANT

Chemistry for Cambridge International AS & A Level Coursebook with Digital Access (2 Years)>Chapter 23 - Entropy and Gibbs Free Energy>EXAM-STYLE QUESTIONS>Q 6

Write a balanced equation to represent the standard free energy change of formation of ethane. Include state symbols in your answer.

When ethanol undergoes combustion, carbon dioxide and water are formed. C2H5OHl+3O2g→2CO2g+3H2Ol. Calculate the standard entropy change for this reaction. Values for S⊝in J K-1mol-1;C2H5OHl=160.7,O2g=205.0,CO2g=213.6,H2Ol=69.90.

Important Questions on Entropy and Gibbs Free Energy

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