A substance has a molar mass of 40.0g/mol. If the decomposition of 1.00mole of this substance absorbs 60.0KJ of energy, how much energy would be absorbed by the decomposition of 20.0g of the substance?

1 Answer
Nov 5, 2015

Answer:

#"30.0 kJ"#

Explanation:

The idea here is that you need to use the given molar mass to determine how many moles you'd get in the #"20.0 g"# sample.

So, a substance's molar mass tells you what the exact mass of one mole of said substance is. In your case, the substance has a molar mass of #"40.0 g/mol"#, which means that every mole will have a mass of #"40.0 g"#.

If that's the case, then you can say that

#20.0color(red)(cancel(color(black)("g"))) * "1 mole"/(40.0color(red)(cancel(color(black)("g")))) = "0.500 moles"#

So, if #"60.0 kJ"# of heat are being absorbed when #1.00# moles undergo decomposition, it follows that the decomposition of #0.500# moles wil require

#0.500color(red)(cancel(color(black)("moles"))) * "60.0 kJ"/(1.00color(red)(cancel(color(black)("mole")))) = color(green)("30.0 kJ")#