Results are out! Find what you Get quick advice or join the chat

Unlock these great extras with your FREE membership

  • One-on-one advice about results day and Clearing
  • Free access to our personal statement wizard
  • Customise TSR to suit how you want to use it

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

Announcements Posted on
Find your uni forum to get talking to other applicants, existing students and your future course-mates 27-07-2015
Win top prizes in our mega results day giveaway... 24-07-2015
  1. Offline

    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?

  2. Offline

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

    Probably an error in print?
  3. Online

    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. Offline

    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. Offline

    (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.
    This - the question is not asking about the enthalpy change.
  6. Offline

    Ok seems most people are saying the negative sign should be there! Cheers!


Submit reply


Thanks for posting! You just need to create an account in order to submit the post
  1. this can't be left blank
    that username has been taken, please choose another Forgotten your password?
  2. this can't be left blank
    this email is already registered. Forgotten your password?
  3. this can't be left blank

    6 characters or longer with both numbers and letters is safer

  4. this can't be left empty
    your full birthday is required
  1. By joining you agree to our Ts and Cs, privacy policy and site rules

  2. Slide to join now Processing…

Updated: May 30, 2009
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

Did you lie on your personal statement?
New on TSR

Results are coming...

No sweat. Here's all you need to make sure you're ready

Study resources

Think you'll be in clearing or adjustment?

Hear direct from unis that want to talk to you

Get email alerts for university course places that match your subjects and grades. Just let us know what you're studying.

Quick reply
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.