Question

Hydrogen is mixed with a stoichiometric amount of oxygen in a 1 L volume at 100 kPa at 300 K. All of the hydrogen is burned at constant but heat leaves the system such that the final temperature is still 300 K. What is the amount of heat released and what is the final pressure in the container?

Answer 1

Calculate moles of Hydrogen and oxygen using PV=nRT

Partila pressure define

P_total = n_total x (RT/V)

100 kPa = n_total x (8.314 L kPa K^-1 mol^-1 x 300 K/1L)

100 kPa = n_total x 2494 kPa mol^-1

n_total = 100 kPa/2494 kPa mol^-1

n_total = 0.04 moles

Since H2 and O2 are mixed stoichiometricall H2 is 0.02 moles

H combustion of hydrogen is −286 kJ/mol

H for 0.02 moles will be 5.72 kJ

Combustion equation is

2H₂(g) + O₂(g) ––> 2H₂O (g)

2 moles of hydrogen burns with 1 mole of oxygen to product 2 moles of water

0.02 moles of hydrogen will consume 0.01 moles of oxygen to give 0.02 moles of water

After combustion all hydrogen is consumed along with 0.01 moles of oxygen finally 0.02 moles of water and 0.01 moles of oxygen are left.

So Pressure can be calculate using the formula described earlier with n_total = 0.03

P_total = n_total x (RT/V)

P_total  = 0.03 x 2494 kPa mol^-1

P_total = 74.8 kPa

SO Heat released is 5.72 kJ and final pressure is 74.8 kPa