Consider the reactions: a→2b(ΔH₁​, 2b→3c(ΔH₂​. What is ΔH for the reaction 3c→a?
a. ΔH=−(ΔH₁​+ΔH₂​)
b. ΔH=ΔH₁​+ΔH₂​
c. ΔH=1/3​(ΔH₁​+ΔH₂​)
d. ΔH=1/3​(ΔH₂​−ΔH₁​)