Question

The reaction of potassium metal with chlorine gas is exothermic and proceeds according to the following chemical equation.

Cl2 (g) + 2K (s) --> 2KCl (s) deltaH*_rxn = -873.0 kJ*mol^-1

Calculate the energy released as heat when 4.54 L of chlorine gas are allowed to react with excess potassium at 25*C and 1.00 bar.

A: -2160 kJ

B: -160 kJ

C: -109 kJ

D: -873 kJ

Answer 1

The given reaction is

2K(s) + Cl₂(g) --> 2KCl(s) for which

Now this heat of reaction has been defined for 1 mole of chlorine gas .

Now we need to find out how much energy will be liberated when 4.54 litres of chlorine gas is allowed to react with excess potassium at 25^oC at 1 bar .

So let us calculate number of moles of Chlorine gas needed to react.

we know PV=nRT

Given P=1 bar ,V=4.54 litres, R=0.08 bar-lit/mol-K ,T=25^oC=298 K

so n=number of moles =PV/RT

n=0.1855 moles

We know for 1 mole of Cl₂ heat liberated is

so 0.1855 moles of Cl₂ heat liberated =0.1855*(-873)=-160 kJ

option B is correct