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# Chemistry Problem...Q=mc(delta)t

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1. Q=mct problem...Chemistry Enthalpy Change!?

Heres the question:
In the experiment, 200g of water were used. The temperature of the water changed from 18 degrees to 68.3 degrees when 1.00g of propane was burnt.

Calculate the energy produced in kJ. The specific heat capacity is 4.18Jg-1K-1.

I did 200x4.18x50.3 and got 42.1 kJ. Then I added a negative sign because it looks exothermic to me (as all combustion reactions are exothermic and temp of surroundings increased), but the mark scheme has no negative sign. Have I got it wrong? Can anyone help me?

Thanks
2. mark scheme is wrong, all exothermic reactions have a negative enthalpy change value.

Probably an error in print?
3. Yeah there should be a negative sign there.

But shouldn't you trying to figure out kj mol-1?

In whic case it would be -1850 kj mol-1
4. Exothermic reactions give out heat, so there will be a positive output of energy from the system to the surroundings (the water). Hence, no minus sign.
5. (Original post by Altocirrus)
Exothermic reactions give out heat, so there will be a positive output of energy from the system to the surroundings (the water). Hence, no minus sign.
6. Ok thanks...it seems most people are saying the negative sign should be there! Cheers!

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