What is the ∆H value for this thermo chemical equation? Full question in the description box below.

enter image source here

2 Answers
Jan 10, 2018

sf(-741color(white)(x)kJ"/""mol")

Explanation:

sf(M_r[C_3H_8]=44.1)

We are told that:

1 tonne gives sf(1.68xx10^4color(white)(x)MJ)

:.sf(cancel(10^6)color(white)(x)grarr1.68xx10^4xxcancel(10^(6))J)

This means that:

sf(1color(white)(x)grarr1.68xx10^4color(white)(x)J)

We need to find the energy released by 1 mole which is 44.1 g:

:.sf(44.1color(white)(x)grarr1.68xx10^4xx44.1color(white)(x)J)

sf(=74.088xx10^4color(white)(x)J)

sf(=741color(white)(x)"kJ")

Since heat is released we can say that:

sf(DeltaH=-741color(white)(x)"kJ""/""mol")

Jan 10, 2018

DeltaH=-739 kJmol^-1

Explanation:

First we need to calculate the number of moles of CO_2 in 1 tonne, which is 10^6 g. The molar mass of CO_2 is 44 gmol^-1.

n=m/M=10^6/44=22,727 mol

Now the total energy produced by 1 tonne is 1.68xx10^4 MJ = 1.68xx10^7 kJ. This is energy emitted to the environment, and therefore lost from the chemical system. That means it will take a negative value when we calculate the DeltaH.

We need to divide this by the number of moles to find the DeltaH value in kJmol^-1.

DeltaH=-(1.68xx10^7)/(22,727)=-739 kJmol^-1