Question

The enthalpy change of which reaction corresponds to $\Delta H_f^o$ for ${Na}_2{CO}_3$ at $298K$?

• A. $2Na\left(s\right)+C\left(s\right)+\frac{3}{2}{O}_2\left(g\right)⟶{Na}_2{CO}_3\left(s\right)$
• B. ${Na}_{2}O\left(s\right)+C{O}_2\left(g\right)⟶{Na}_2{CO}_3\left(s\right)$
• C. $2{Na}^{+}(aq.)+{CO}_3^{2-}(aq.)⟶{Na}_2{CO}_3\left(s\right)$
• D. $2{Na}^{+}(aq.)+2{OH}^{-}(aq.)+C{O}_2(aq.)⟶{Na}_2{CO}_3\left(s\right)+H_{2}O$

Answer 1

The correct option is A $2Na\left(s\right)+C\left(s\right)+\frac{3}{2}{O}_2\left(g\right)⟶{Na}_2{CO}_3\left(s\right)$

The enthalpy change for the formation of 1 mol of a compound from its component elements when the component elements are each in their standard states. The standard enthalpy of formation of any element in its most stable form is zero by definition.

So, A is the correct option.