Gases State Worksheet 1 Answers

Suggested Answer 1 (a) (i)

Let number of moles of H2 be x; number of moles of CH4 = 1.5 x x(2) + 1.5x(12 +4) = 5 26x = 5, x = 0.1923 Total number of moles of gas = 0.1923 + 1.5 (0.1923) = 0.4808 PV = nRT, PT = (0.4808) (8.31)(273+20)/(250 x 10-6) = 4.683 x 106 Pa PCH 4 = [(1.5(0.1923))/(0.4808)] x 4.683 x 106 = 2.81 x 106 Pa PH 2 = (0.1923/0.4808) x 4.683 x 106 = 1.87 x 106 Pa

(ii)

ƒ

The gas particles have negligible intermolecular forces.

ƒ

The gas particles are point sized, volumes of the gas particles is negligible

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The gas particles do not react with each other chemically. (Dalton’s Law)

(iii) ƒ

CH4 and H2 are non-polar molecules with id-id interactions as IMF. It is the weakest form of IMF, hence it is taken to be negligible. It is impossible for CH4 and H2 to react with each other chemically.

ƒ (iv)

PV/RT CH4

n ideal

(b) (i) (ii)

CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (l) Bond Energy of H-H = 436 kJ mol-1 ∆Hatom (H) = ½ x (+436) = +218 kJ mol-1

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(iii)

C (s)

+

2H2 (g)

ΔHf

4ΔHatom (H)

ΔHatom (C)

C (g)

+

CH4 (g) 4 BE (C-H)

4H (g)

BE (C-H) = ¼ ((+716.7) + 4(218) – (-74.8)) = +416 kJ mol-1 (iv)

The Data Booklet’s value is smaller than the calculated value. It is because the former in an average value of the BE of C-H, where other constituent atoms found in a molecule that contains a C-H bond will weaken the bond. OR The difference between (iii) and Data Booklet value is small and hence, it is a good means to obtain the BE of C-H.

(c)

(i) x x

xx

O

xx

N

xx xO x xx

Shape: Bent (ii)

N in NO2 has an unpaired electron. Hence, two NO2 molecules can react with each other to get N2O4. Thus, this cause NO2 to deviate from ideality as we will not be able to get p α n, for constant T since there is possibility that at a certain T, it causes the 2 NO2 to react with each other and hence reduce the number of gas particles, thus giving an inaccurate projection of the amount of pressure the gas exerts.

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