C2H4 (g) + 3 O2 (g) ––�?gt; 2 CO2 (g) + 2 H2O (l) ΔH° = �?411 kJ
What this balanced reaction says is this: One mole of ethylene reacts with three moles of oxygen to form two moles of carbon dioxide, two moles of water, and 1411 kJ of heat.
So, if one mole of ethylene produces 1411 kJ of heat, how many moles of ethylene will produce 430.4 kJ of heat?
You can do this like a conversion problem, "given" value X conversion factor(s) = "desired" value. The "given" value is 430.4 kJ. The "desired" value is the moles of ethylene. The conversion factor comes from the reaction,
"1411 kJ per 1 mol C2H4" or "1 mol C2H4 per 1411 kJ"
1411 kJ or 1 mol C2H4
mol C2H4 1411 kJ
We want to use the conversion factor that gives the correct units (moles of C2H4) in the end:
430.4 kJ X 1 mol C2H4 =
1 1411 kJ
kJ units cancel, leaving us with moles of C2H4. 
Convert moles of C2H4 to grams, and that's it!
The second problem is very similar.
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