Name: PART (Multiple choice; mark your answers on page 1) (1 mark each 10 marks)

Question

Name: PART (Multiple choice; mark your answers on page 1) (1 mark each 10 marks) 1. Equilibrium is reached in chemical reactions when a) b) c) d) e) The rates of the forward and reverse reactions become equal. The concentrations of reactants and products become equal. The temperature shows a sharp rise. All chemical reactions stop The forward reaction stops. 2. At 2000 ., K . 0.010 for the reaction: Predict what will happen after 0.40 moles N2, 0.10 moles O2 and 0.080 moles NO are placed in a 1.0 L container at 2000-C. a) The system remains unchanged b) The concentration of NO will decrease; the concentrations of N2 and O2 will increase. c) The concentration of NO will increase; the concentrations of N2 and O2 will decrease. d) The concentration of NO will decrease, the concentrations of and 02 will remain Nig) + 0210 2 No,o. unchanged. e) More information is necessary 3 Hz0g) 2 NHig. for which Ammonia is prepared by the reaction H-92.2 kJ and K-4.0x 108 at 25 C. What happens after temperature is increased to 500 *C? a) K increases. b) The equilibrium concentration of NHs increases. c) The equilibrium concentration of NHs decreases. d) The reaction of N2 with H2 to form ammonia is endothermic. e) None of the above statements is true. 3. N2(g) + 4. Consider the reaction represented by the equation 2 S02(8+0r) 2 S03 For the system at chemical equilibrium, which of the following explains what happens after the addition of oxygen gas (assume constant temperature)? a) The concentration of SO, increases and the value of K increases. b) The concentration of SOs decreases and the value of K increases c) The concentration of SOs stays the same and the value of K decreases. d) The concentration of SOs decreases and the value of K stays the same. e) The concentration of SO, increases and the value of K stays the same

Explanation / Answer

1)

When rate of forward reaction equals to rate of backward reaction the reaction will be at equilibrium so answer is

(a) rates of forward and reverse reactions become equal

2)

Given

[O2] = 0.1 moles / 1 L = 0.1

[N2] = 0.4 moles / 1 L = 0.4

[NO] = 0.080 moles / 1 L = 0.08

Q = (0.08)2 / 0.1*0.4 = 0.64

Given K = 0.01

Q> K

so equilibrium will shift towards right more products will be formed

(c) Concentration of NO will increase, concentration of N2 and O2 will decrease

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