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CHEM191

Problem Sheet 1 – Stoichiometry, Solvation and Equilibria

1.

NaCl with sulfuric acid, H2SO4, to produce sodium sulfate, Na2SO4, as described by the following equation: 2NaCl + H2SO4 à Na2SO4 + 2HCl (a)

Which of the following statements about this reaction, when it goes to completion, is INCORRECT? (A) (B) (C) (D)

2.

When 2 moles of NaCl react, 2 moles of HCl are produced. When 5 moles of H2SO4 react, 10 moles of HCl are produced. When 1 mole of NaCl reacts, 2 moles of Na2SO4 are produced. When 4 moles of Na2SO4 are produced, 8 moles of HCl are produced.

(b)

If 32.0 g of NaCl reacts with excess H2SO4 how many moles of HCl will be produced?

(c)

If 17.0 g of NaCl react with excess H2SO4, what mass of Na2SO4 will be produced?

(d)

If 48.0 g of NaCl react with 19.0 g of H2SO4, what mass of Na2SO4 will be produced?

Copper is obtained from sulfide ores, such as chalcocite, Cu2S, by a multi-step process. After grinding the ore, it is ‘roasted’ (heated strongly in oxygen gas) to form Cu2O and gaseous sulfur dioxide. (a)

Write a balanced chemical equation for the roasting reaction.

(b)

Calculate the amount (in moles) of oxygen gas that is required to roast 10.0 g of Cu2S.

(c)

Calculate the mass (in grams) of sulfur dioxide which is formed when 10.0 g of Cu2S is roasted. [Silberberg 6e, McGraw Hill, 2012]

3.

Explain the following observations in terms of the attractive interactions between the molecules. (a)

Sodium chloride, NaCl, is soluble in water.

(b)

Oxygen gas is soluble in water.

(c)

Ice has a lower density than liquid water.

4.

5.

Write equilibrium constant expressions for each of the following. (a)

2NO2(g) ⇌ N2O4(g)

(b)

H2(g) + I2(g) ⇌ 2HI(g)

(c)

H2(g) + S(s) ⇌ H2S(g)

(d)

NH3(g) + H2O(l) ⇌ NH4+(aq) + OH-(aq)

(e)

Zn2+(aq) + 4NH3(aq) ⇌ Zn(NH3)42+(aq)

The equilibrium constant expression for a reaction is Kc =

[ "#$ ] '&[#$ ]& [ "$ #(] $&

Write the balanced chemical equation for this equilibrium reaction.

6.

When CO(g) reacts with H2(g), CH4(g) and H2O(g) is formed in an equilibrium mixture. CO(g) + 3H2(g) ⇌ CH4(g) + H2O(g) In one experiment the equilibrium concentrations of these were found to be: [CO]e = 0.0613 mol L-1

[H2]e = 0.1839 mol L-1

[CH4]e = 0.0387 mol L-1

[H2O]e = 0.0387 mol L-1

What is the value of Kc for this reaction?

7.

Sulfuryl chloride, SO2Cl2, decomposes according to the following endothermic reaction: SO2Cl2(g) ⇋ SO2(g) + Cl2(g)

Kc = 2.95´108 at 298 K

(a)

Write an expression for the equilibrium constant for the reaction.

(b)

Describe how the equilibrium concentration of the Cl2(g) is affected by: (i)

Adding more SO2(g) to the system at equilibrium

(ii)

Adding more SO2Cl2(g) to the system at equilibrium

Give your reasoning in each case

8.

At a certain temperature, the reaction: CO(g) + H2O(g) ⇌ CO2(g) + H2(g) has Kc = 0.400. Exactly 1.00 mol of each gas was placed in a 100 L flask and the mixture underwent reaction. Calculate Qc for the mixture initially and determine which way the position of equilibrium must move for the reaction to reach equilibrium (ie when the reaction starts, does CO(g) react with H2O(g) or does CO2(g) react with H2(g)?)

9.

NOTE: this question is more challenging and beyond what you will need to be able to do for the exams. For the equilibrium I2(g) + Cl2(g) ⇋ 2ICl(g)

Kc = 82

0.1 mol of I2(g) and 0.1 mol of Cl2(g) are placed in a 1 L flask and the reaction allowed to reach equilibrium. (a)

Write an expression for the equilibrium constant for the reaction.

(b)

Calculate the equilibrium concentrations of each of the species in the equilibrium....