Question

When $1$ mole of sulfur burns to form $S{O}_2$, $1300$ calories are released. When $1$ mole of sulfur burns to form $S{O}_3,3600$ calories are released. What is $△H$ when $1$ mole of $S{O}_2$ burns to form $S{O}_3$?

• A. $3900cal$
• B. $-1950cal$
• C. $1000cal$
• D. $-500cal$
• E. $-2300cal$

Answer 1

The correct option is E $-2300cal$

According to the question,

$S+O_2⟶S{O}_2$ ; $△H=-1.3KCal$

$S+\frac{3}{2}{O}_2⟶S{O}_3$ ; $△H=-3.6KCal$

Also, $S{O}_2+\frac{1}{2}{O}_2⟶S{O}_3$ ; required equation.

So, to get the required equation;

Flip first equation, changing the sign of $△H$

$S{O}_2⟶S+O_2$ ; $△H=1.3KCal$

$S+3/2O_2⟶S{O}_3$ ; $△H=-3.6KCal$

When we add, these equations , we get

$S{O}_2+1/2O_2⟶S{O}_3$

Therefore, $1.3+(-3.6)=-2.3KCal$

$=-2300KCal$