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Context for question 3

White phosphorus is composed of P

_{4}

molecules with a tetrahedral structure, as shown in the diagram on the left. Each P atom is bonded to the other three P atoms by single bonds, as shown in the incomplete Lewis diagram on the right.

Tetrahedral structure of the P4 molecule

3(A)Covalent Bonding, Lewis Structures and Molecular ShapeEasy1 mark

In the box in part A, complete the Lewis diagram for P

_{4}

by drawing the nonbonding electrons.

Context for 3(B)

The reaction of white phosphorus with oxygen to form P

_{4}

_{10}

(s) is thermodynamically favorable at 298 K. The reaction is represented by equation 1.

Equation 1:

P_{4} (s) + 5 O_{2} (g) \to P_{4} O_{10} (s)

3(B)(i)Entropy, Gibbs Energy and FeasibilityEasy1 mark

The entropy change of the reaction,

Δ S_{r x n}^{\circ}

, is negative. Using particle-level reasoning, explain why the entropy decreases as the reaction progresses.

3(B)(ii)Entropy, Gibbs Energy and FeasibilityMedium1 mark

The enthalpy change of the reaction,

Δ H_{r x n}^{\circ}

, is also negative. A student claims that the favorability of the reaction is driven by enthalpy and not by entropy. Is the student's claim correct? Justify your answer by using the relationship between

Δ G_{r x n}^{\circ}

Δ H_{r x n}^{\circ}

, and

Δ S_{r x n}^{\circ}

Context for 3(C)

_{4}

_{10}

(s) reacts exothermically with water to form phosphoric acid, as represented by equation 2.

Equation 2:

P_{4} O_{10} (s) + 6 H_{2} O (l) \to 4 H_{3} P O_{4} (aq)

A chemist uses a calorimetry experiment to determine the enthalpy change for the reaction, as represented by the following diagram.

Calorimetry apparatus: thermometer, stirrer, insulating cover, inner vessel and outer vessel

The chemist carries out the calorimetry experiment and records the following information.

Quantity	Value
Mass of P $_{4}$ O $_{10}$	0.100 g
Mass of H $_{2}$ O	100.0 g
Initial temperature	22.00 $^{\circ}$ C
Final temperature	22.38 $^{\circ}$ C
Molar mass of P $_{4}$ O $_{10}$	283.9 g/mol
Specific heat of H $_{2}$ O	4.18 J/(g· $^{\circ}$ C)

3(C)Enthalpy Changes, Calorimetry and Hess's LawMedium3 marks

i. Calculate the amount of heat, q, released during the experiment, in kJ. Assume that the specific heat of the solution is the same as that of water.

ii. Calculate the value of

Δ H_{r x n}^{\circ}

for equation 2 in kJ/mol

_{r x n}

. Include the sign in your answer.

3(D)Enthalpy Changes, Calorimetry and Hess's LawMedium1 mark

The chemist weighed out 0.100 g of P

_{4}

_{10}

and 100.0 g of H

_{2}

O to perform a second trial. In the second trial, some of the solid P

_{4}

_{10}

stuck to the weighing paper and was not transferred to the calorimeter. Given that P

_{4}

_{10}

is the limiting reactant, would

Δ H_{r x n}^{\circ}

for the second trial be greater than, less than, or equal to the value in the first trial? Justify your answer.

Context for 3(E)

_{4}

(s) also reacts readily with Cl

_{2}

(g) to produce phosphorus trichloride, PCl

_{3}

(g), which in turn reacts with Cl

_{2}

(g) in an equilibrium process to produce PCl

_{5}

(g). The reactions are represented by equations 3 and 4.

Equation 3:

P_{4} (s) + 6 C l_{2} (g) \to 4 PC l_{3} (g)

with

Δ H_{r x n, 1}^{\circ} = - 1148

kJ/mol

Equation 4:

PC l_{3} (g) + C l_{2} (g) ⇌ PC l_{5} (g)

with

Δ H_{r x n, 2}^{\circ} = - 88

kJ/mol

3(E)Enthalpy Changes, Calorimetry and Hess's LawEasy1 mark

Calculate the standard enthalpy of formation of PCl

_{5}

(g) represented by equation 5.

Equation 5:

\frac{1}{4} P_{4} (s) + \frac{5}{2} C l_{2} (g) \to PC l_{5} (g)

with

Δ H_{f}^{\circ} = ?

Context for 3(F)

Equation 4 for the reaction that occurs is shown.

Equation 4:

PC l_{3} (g) + C l_{2} (g) ⇌ PC l_{5} (g)

with

Δ H_{r x n, 2}^{\circ} = - 88

kJ/mol

The following particle-level diagram represents the contents of the vessel in an equilibrium mixture at 546 K involving equation 4.

Particle diagram of an equilibrium mixture of Cl2, PCl3 and PCl5 particles at 546 K

3(F)(i)Chemical Equilibrium: Le Chatelier, Kc, Kp and CalculationsEasy1 mark

If each particle in the diagram represents a partial pressure of 1.00 atm, what is the value of

K_{p}

for the equilibrium mixture at 546 K?

3(F)(ii)Chemical Equilibrium: Le Chatelier, Kc, Kp and CalculationsMedium1 mark

Does the value of

K_{p}

increase, decrease, or remain the same when the temperature is increased to 596 K? Justify your answer based on

Δ H_{r x n, 2}^{\circ}