Question #f93f3
1 Answer
The answer is (d)
Explanation:
The idea here is that you can play around with your reactions to try and find a relationship between the first one and the other two.
Notice that you have
#"A" + "B" -> "C" + "D"# #" "color(blue)((1))#
but that the two other reactions have
#"C" + "X" -> "A" + "Y"# #" "color(blue)((2))#
#"D" + "Y" -> "B" + "X"# #" "color(blue)((3))#
If you add reactions
#"C" + color(red)(cancel(color(black)("X"))) + "D" + color(red)(cancel(color(black)("Y"))) -> "A" + color(red)(cancel(color(black)("Y"))) + "B" + color(red)(cancel(color(black)("X")))#
#"C" + "D" -> "A" + "B"# #" "(DeltaH_2 + DeltaH_3)#
This is none other than the reverse reaction for reaction
For a general chemical reaction that has the enthalpy change of reaction
#DeltaH_"reverse" = - DeltaH_"forward"#
In this case, you have
#"A" + "B" -> "C" + "D"# ,#" "DeltaH_1#
and
#"C" + "D" -> "A" + "B"# #" "(DeltaH_2 + DeltaH_3)#
This means that you have
#DeltaH_1 = -(DeltaH_2 + DeltaH_3)#
Rearrange this to get
#DeltaH_1 = - DeltaH_2 - DeltaH_3 implies color(green)(DeltaH_3 = -DeltaH_1 - DeltaH_2)#