Question

just wanted to ask. if this is the question, you'll DIRECTLY cancel out and bring down? i mean, you don't have to mind the right places of the reactants and the products? What is the balanced overall equation for the following process( equation 3) and what is the ∆Hoverall?
(1) P4(s) + 6Cl2(g) ---> 4PCl3 (g) ∆H= -1148 kJ
(2) 4PCl3(g) + 4Cl2 (g) ---> 4PCl5(g) ∆H= -460 kJ
(3) ? ∆Hoverall= ?

Answer 1

when adding chemical reactions, try to treat them as if they were regular algebraic equations, with the reaction arrow --> being equivalent to the equals sign. So if you add those two reaction together, take the reactants and keep them as reactants, and take the products, and keep them as products\[P_4(s) + 6Cl_2(g) + 4PCl_3(g) + 4Cl_2(g) \rightarrow 4PCl_5(g)\] since you have some common terms, we can combine them
\[P_4(s) + 10Cl_2(g) + 4PCl_3(g) \rightarrow 4PCl_5(g)\] The DH of the reaction is done the exact same way: add the pieces together

Answer 2

I think you forgot to cancel the PCl3, @JFraser.

Answer 3

@ienarancillo, if your question is: Does it matter in what order the reactants are written, e.g. is P4(s) + 6Cl2(g) different from 6Cl2(g) + P4(s)? Then the answer is no, the order does not matter. P4(s) + 6Cl2(g) is exactly the same as 6Cl2(g) + P4(s).

Answer 4

@Carl_Pham quite right, thanks!