Question

1. using the following reactions, calculate the heat of formation, δhf, of cs₂ using hess law. show all your work.

i. c(s) + o₂(g) → co₂(g) δh = -393.3 kj
ii. s(s) + o₂(g) → so₂(g) δh = -293.72 kj
iii. cs₂(ℓ) + 3 o₂(g) → co₂(g) + 2 so₂(g) δh = -1108.76 kj

Explanation:

Step1: Manipulate the given reactions

The formation reaction of \(CS_2\) is \(C(s)+2S(s)\to CS_2(l)\).
Multiply reaction (ii) by \(2\): \(2S(s) + 2O_2(g)\to2SO_2(g)\), \(\Delta H=2\times(- 293.72\ kJ)=-587.44\ kJ\)
Reverse reaction (iii): \(CO_2(g)+2SO_2(g)\to CS_2(l)+3O_2(g)\), \(\Delta H = 1108.76\ kJ\)

Step2: Add the manipulated reactions and reaction (i)

\(C(s)+O_2(g)\to CO_2(g)\), \(\Delta H=-393.3\ kJ\)
\(2S(s)+2O_2(g)\to2SO_2(g)\), \(\Delta H=-587.44\ kJ\)
\(CO_2(g)+2SO_2(g)\to CS_2(l)+3O_2(g)\), \(\Delta H = 1108.76\ kJ\)

Adding them together:
\(C(s)+2S(s)\to CS_2(l)\)
\(\Delta H=(-393.3)+(-587.44)+1108.76\)

Step3: Calculate the heat of formation

\(\Delta H=(-393.3 - 587.44+1108.76)\ kJ\)
\(\Delta H = 128.02\ kJ\)

Answer:

\(128.02\ kJ\)