Question

Solid carbon can react with gaseous water to form carbon monoxide gas and hydrogen gas. The equilibrium constant for the reaction at 700.0 K is Kp=1.60×10−3. If a 1.55-L reaction vessel initially contains 247 torr of water at 700.0 K in contact with excess solid carbon, find the percent by mass of hydrogen gas of the gaseous reaction mixture at equilibrium.

Answer 1

247 torr is divided with 760 torr/atm to obtain 0.325 atm

	H2O	CO	H2
Initial partial pressure (atm)	0.325	0	0
Change in partial pressure (atm)	-x	x	x
Equilibrium partial pressure (atm)	0.325-x	x	x

0.325 - x can be approximated to 0.325 as Kp value is small

This is a quadratic equation with roots x= 0.022, x = -0.0236

The negative value is discarded as pressure cannot be negative.

Hence, the equilibrium partial pressures are

For water,

For CO,

For H2,

The percent by mass of hydrogen gas of the gaseous reaction mixture at equilibrium %