In: Chemistry
Given the following thermochemical equations:
X2+3Y2 equals 2XY3 and Delta H =-340 kJ
X2+2 Z2 equals 2XZ2 and Delta H = -170 kJ
2Y2 + Z2 equals 2Y2Z and Delta H=-260kJ
Calculate the change in enthalpy for the following reaction
4XY3+7 Z2 equals 6Y2Z+4XZ2
inverting equation #1..
2 XY3 -----> X2 + 3Y2... dH = +340 kJ.
and then multiplying by 2
4 XY3 ----> 2X2 + 6 Y2... dH = +680kJ
=============>1
now you have 4 XY3 on the left.. as you need..
now you need to get rid of the 2 X2 on the right
2 x equation #2 will do that
2X2+4 Z2 -------> 4XZ2 and Delta H = -340 kJ=============>2
3 x equation #3
6Y2 +3Z2 ,------>6Y2Z and Delta H=-780kJ===========>3
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adding eqns
4 XY3 ----> 2X2 + 6Y2... dH = +680kJ ======>1
2X2+4 Z2 -------> 4XZ2 and Delta H = -340 kJ===>2
6Y2 +3Z2 ,------>6Y2Z and Delta H=-780kJ===>3
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4 XY3 +7Z2 ----------->6Y2Z+ 4XZ2
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+680-340-780
-440kJ