# Calculating reaction enthalpy given other reactions

\begin{alignat}{2}\ce{X(s) + 1/2O2(g) &-> XO}&&\qquad\Delta H=-895.5\ \mathrm{kJ} \\ \ce{XCO3(s) &-> XO(s) + CO2(g)}&&\qquad\Delta H= +484.3\ \mathrm{kJ}\\ \ce{X(s) + 1/2O2(g) + CO2 &-> XCO3(s)}&&\qquad\Delta H = \;?\ \mathrm{kJ} \end{alignat}

I wish to know how to do it. I have seen some questions where there's 3+ equations and at the end a final equation that I would need to determine the $\Delta H$ for the final equation. I have looked online on how to solve this but the tutorials are very confusing and I can't understand them. Can someone explain how to do this and other similar problems like this?

One of the tutorials talks about making sure they cancel out and flipping the equations? Can someone please explain this?

• Well, that's pretty much about it: you can cancel things out and flip the equations, just like you would do in algebra, say, with $x=x^2+x-1$. – Ivan Neretin Oct 15 '15 at 8:37
• @IvanNeretin Ok but why would you need to flip it? Like can you explain step by step how to solve these types of problems? I'm totally lost here. – user3882522 Oct 15 '15 at 8:44
• @surelyourejoking I'm assuming that's not proper formatting, but that's how I think of chemical equations in my head, as equations. But can you please explain how to solve these types of problems step by step? – user3882522 Oct 15 '15 at 8:47
• Flip the second equation, add it to the first, cancel out whatever you can. See where this gets you. – Ivan Neretin Oct 15 '15 at 8:48
• @IvanNeretin Ok so under what conditions would I need to flip an equation? Is there anyway to tell when I will need to flip an equation? I mean thank you for telling me what to do to solve it but I want to understand the topic so I can apply it to other problems – user3882522 Oct 15 '15 at 8:52