AP Chemistry· difficulty 4/5
Given: (1) C(s) + O(g) → CO(g), ΔH = -394 kJ; (2) H(g) + ½O(g) → HO(l), ΔH = -286 kJ; (3) CH(g) + 2O(g) → CO(g) + 2HO(l), ΔH = -891 kJ. ΔH for C(s) + 2H(g) → CH(g) is
-211 kJ
-75 kJ ((1) + 2×(2) − (3))
+75 kJ
-1857 kJ
Explanation
Target = (1) + 2(2) − (3) = -394 + 2(-286) − (-891) = -394 − 572 + 891 = -75 kJ.
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