Well, not there yet! You should write the four reactions you are adding together, with their ΔHs, so we can both see how they add up to give the desired reaction. I think we may have a copy of you textbook at school, but I didn't have a chance to look for it. It should have a few examples of doing this under "Hess's law."
Remember, if the same thing is on both sides, they "cancel." That's not the best way to word it, but here's an example:
NH4Cl (s) ––�?gt; NH4Cl (aq) ΔH = +15428.82 J/mol
NH4Cl (aq) ––�?gt; NH3 (aq) + HCl (aq) ΔH = +44718.6 J/mol <–�?Note the sign change since this reaction was reversed.
NH4Cl (s) ––�?gt; NH3 (aq) + HCl (aq) ΔH = +60147.42 J/mol
See how the NH4Cl (aq)s "cancel"? When you add the reactions together, there is one NH4Cl (aq) on each side. Like an algebra equation with "5x" on each side. You can subtract 5x from each side and simplify the equation. We can do likewise with chemical equations. The yield sign is like the "equals" sign.
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