The reaction AB( a q )?A( g )+B( g ) is second order in AB and has a rate consta

Question

The reaction AB(aq)?A(g)+B(g) is second order in AB and has a rate constant of 0.0171 M?1?s?1 at 25.0 ?C. A reaction vessel initially contains 250.0 mL of 0.107 M AB which is allowed to react to form the gaseous product. The product is collected over water at 25.0 ?C.

Part A

How much time is required to produce 117.0 mL of the products at a barometric pressure of 775.1 mmHg . (The vapor pressure of water at this temperature is 23.8 mmHg.)

The reaction AB(aq)?A(g)+B(g) is second order in AB and has a rate constant of 0.0171 M?1?s?1 at 25.0 ?C. A reaction vessel initially contains 250.0 mL of 0.107 M AB which is allowed to react to form the gaseous product. The product is collected over water at 25.0 ?C.

Part A

How much time is required to produce 117.0 mL of the products at a barometric pressure of 775.1 mmHg . (The vapor pressure of water at this temperature is 23.8 mmHg.)

Explanation / Answer

Volume of product = 117.0 mL = 0.117 L

Pressure of products = 775.1 - 23.8 = 751.3 mmHg = 751.3 / 760 = 0.988 atm

R = 0.0821 L.atm.K-1.mol-1

T = 25 + 273.15 = 298.15 K

Assuming idela g=behaviour,

P V = n R T

n = 0.988 * 0.117 / (0.0821 * 298.15)

n = 0.00472 mol

Therefore,

moles of AB reacted = 0.00472 / 2 = 0.00236 mol

Initial moles of of AB = 0.107 * 250 / 1000 = 0.0268 mol

Remaining moles of AB = 0.0268 - 0.00236 = 0.0245 mol

For a second order reaction,

1 / [A] = kt + 1/[A]0

1 / 0.0245 = 0.0171 * t + 1 / 0.0268

t = 204.8 s

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