Physical Chemistry Answers

Topic: Electrode Potential and Electrochemical Cells

question 1

The diagram below shows the experiment setup for a typical electrochemical cell that contains two standard half cells. The cell operates according to the reaction represented by the following equation

Zn(s) + Ni²⁺ (aq) —> NI(s) + Zn²⁺ (aq)

a) identify M and M²⁺ in the diagram? ( marks)

b) indicate which of the metal electrodes in the cathode. Write the balanced equation for the reaction that occurs in the half-cell containing the cathode. (2 marks).

c) Describe what would happen in the cell voltage if the said bridge was removed. Explain the reason for this. ( 2 marks)

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Topic:Acid and Bases

Q1

a) calculate the pH of the following solutions:

i) 0.002 mol dm^-3 KOH (2 marks)

ii) 0.10 mol dm^-3 C₆H₅COOH ( K of benzoin acid = 6.3 x 10^-5 mol dm^-3 ) ( 4 marks)

b) The pH of a 0.10 mol dm^-3 solution of a weak mono proton acid, HA , is 2.85. Determine the K of the acid. ( 2 marks)

c) A 500 cm³ solution containing 1.8g of a weak acid HA has a pH of 3.5. Calculate the molar mass of the acid, given that it has a value for K of 2.0 x 10 ^-6mol dm . ( 5 marks)

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. Under 298 K and 101.325 kpa, the defined entropy of diamond and graphite is 2.45 J· mol^-1·K^-1 and 5.71 J· mol^-1·K^-1, respectively. Their standard combustion heat are

-395.40 kJ · mol^-1and -393.51 kJ·mol^-1, respectively. Calculate the value of

Graphite          Diamond

under these conditions, and explain which crystal is more stable at these conditions.

Acids and Bases

Q1

a) State weather the following species can behave as an acid, as a base , or both:

(i) NH₄⁺

(ii) HCIO₄

(iii) CO₃^2-

all 1 mark

b) in the following reaction, identify the reactant that acts as an acid:

CH₃COOH (aq) + HCIO₄ (aq) —-> <—- CH₂COOH₂⁺ (aq) + CIO₄ (aq) (1 mark)

c) identify the acid-base conjugate pairs in the following reactions:

HCO₃^- (aq) + H₃O⁺ (aq) —-> <—- CO₂ (g) + H₂O + H₂O (I). ( 2 marks )

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Equilibrium Constant

Q1

for both of the following equilibria, write the expression for the equilibrium constant K_c and state it’s units:

i) H₂(g) + I₂ (g) —-> <—— 2HI (g) (2 marks)

ii) 2SO₂ (g) + O₂(g) ——> <—— 2SO₂ (g) (2 marks)

Q2

the reaction for the formation of hydrogen bromine does not go to completion but reaches an equilibrium, as shown:

H₂(g) + Br₂ —-> <—— 2HBr(g)

a mixture of 1.9 mol of H₂ and 1.9 of Br was prepared and allowed to reach equilibrium in a closed vessel on 250 cm³ capacity. The resulting equilibrium mixture was found to contain 3.0 moles of HBr. Calculate the value of K. (3 marks please detailed answers with explanation🙏🏾🙏🏾🙏🏾🙏🏾)

Topic: Rate Equations

Question 1

Twi compounds, A and B , react in the following way:

A + 3B —> AB₃.

using the data below, derive the rate equation for this reaction and explain your reasoning.(4 marks)

b) Use the experimental data provided below to determine the rate constant. ( 3 marks)

data:

• Experiment 1 ,Initial (A) ( mol dm^-3) 0.100 , Initial (B) (mol dm³ ) 0.100 , Initial rate of formation of AB (mol dm^-3)0.002.
• Experiment 2, Initial (A) (mol dm^-3) 0.100 , Initial (B) ( mol dm^-3) 0.200, Initial rate of formation of AB₃ ( mol dm^-3) 0.008.
• Experiment 3 , Initial (A) (mol dm^-3) 0.100 , Initial (B) (mol dm^-3) 0.300, Initial rate of formation of AB₃ (mol dm^-3) 0.018.
• Experiment 4, Initial (A) ( mol dm^-3) 0.200 , Initial (B) ( mol dm^-3) 0.100 , Initial rate of formation of AB ( mol dm^-3) 0.004.
• Experiment 5, Initial (A) (mol dm^-3) 0.300 , Initial (B) (mol dm^-3) 0.100 , Initial rate of formation of AB (mol dm^-3) 0.006.

Rate Equation

Q1

a) Explain the meaning of the term rate of reaction (1 mark)

b) The following data is provided for the reaction

2NO(g) + H₂(g) ——> N₂O (g) + H₂O

• Initial (NO) (mol dm^-3 ) 0.70 , Initial (H) ( mol dm^-3) 0.42, Initial rate ( mol dm^-3 s^-1) 4.0 x 10^-3.

• Initial (NO) ( mol dm^-3) 1.40, Initial (H) (mol dm^-3) 0.42, initial rate ( mol dm^-3 s^-1) 1.6 x 10^-2.

• Initial (NO) (mol dm^-3)1.40, Initial (H₂) ( mol dm^-3) 0.84, Initial rate (mol dm^-3 s^-1) 1.6 x 10^-2.

(I)use the data to derive the order of reaction with respect to H and NO and explain your workings? (4 marks)

(II)Derive the overall order? (1 mark)

(III)Give the rate equation? (1 mark)

(IV)Calculate the value of k? (2 marks)

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Thermodynamics

Q3

using the following data, calculate the change in entropy when one mole of ammonia is formed from its elements:

N(g) = 191.6 J K mol

H(g) = 130.6 J K mol

NH (g) = 192.3 J K mol

(3 marks please answers with detailed explanation please 🙏🏾 )

Thermodynamics

Q2

using the following data, calculate the enthalpy of solution chloride:

Enthalpy of hydration of Li⁺ = -520 kJ mol-1

Enthalpy of hydration of CI^- = -364 kJmol -1

Lattice enthalpy LiCI = -860 kJ mol-1

(2 marks)

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Topi:Thermodynamics 

Q1

Given the following bond energy data: (Bond and AH_b kJmol-1)

• Bond C-H and AH_b +413 kJmol-1
• Bond C-Br and AH_b +285 kJmol-1
• Bond C-CI and AH_b +328 kJmol-1
• Bond Br-Br and AH_b +193 kJmol-1
• Bond C-C and AH_b +347 kJmol-1

• Bond C=C and AH_b +611 kJmol-1

• Bond H-CI and AH_b +428 kJmol-1
• Bond CI-CI and AH_b +428 kJmol-1

Calculate the theoretical enthalpy changes for the following reactions:

a) C2H4 + Br2 —> C2H4Br2

b) CH4 + CI2 ——> CH3CI + HCI

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