Question

For the reaction: $C_3H_8(g)+5O_2(g)→3CO_2(g)+4H_2O(l)$ at constant temperature, ∆H–∆E is:

• A. RT
• B. -3RT
• C. 3RT
• D. -RT

Answer 1

Answer: (B)

-3RT

Answer 2

Mathematically, it can be represented as:
∆H - ∆E = ∆nRT
In this reaction:
The number of moles of gas molecules on the left side (reactants) is 1 (C3H8) + 5 (O2) = 6 moles.
The number of moles of gas molecules on the right side (products) is 3 (CO2).
So, ∆n = (moles of products) - (moles of reactants) = 3 - 6 =-3 moles.
Now,
∆H - ∆E = ∆nRT = (-3)RT = - 3RT

So, the correct answer is (B): -3RT