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# Energetics help! Watch

1. I need help with an enthalpy change question, I literally have no idea where to start with it, please explain!!

A vessel and its contents of total heat capacity 120 J K–1 were heated using a methane burner. Calculate the maximum theoretical temperature rise when 0.10 g of methane was completely burned. The standard enthalpy of combustion of methane is –890 kJ mol–1. (4 marks)
2. (Original post by LucyQ)
I need help with an enthalpy change question, I literally have no idea where to start with it, please explain!!

A vessel and its contents of total heat capacity 120 J K–1 were heated using a methane burner. Calculate the maximum theoretical temperature rise when 0.10 g of methane was completely burned. The standard enthalpy of combustion of methane is –890 kJ mol–1. (4 marks)
First find out how many moles of methane you have, and how much energy it would produce if burnt.
3. Hey
In the beginning this question looks quite scary but it's not actually.

1) First you should know about the equation Q=mc delta t

2) The question asks you to find change in temperature which is basically delta t.

3) So you rearrange the equation to find delta T. So you get
Delta T= Q/mc

4) Then you just need to find Q, which is heat energy of the methane. You know that enthalpy of combustion is -890Kj per 1 mole.

5) So u need to find the number of moles of methane so that you can multiply it by -890Kj in order to find Q.

6) to find number of moles of methane you do mass/Mr which is 0.1/16=0.00625 moles.
Multiply moles by -890 gives 0.00625*-890=-5.5625.

7) so now u have all the numbers to put into the equation.
Delta t=Q/mc
c is heat capacity.
mc= 0.1*120=12
Delta T= -5.5625/12=-0.464 (it's negative as it's an exothermic reaction)

So temperature rise would be 0.0464 degrees celcius.
Hope this helped

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Updated: April 9, 2013
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