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energy change

when calculatin the energy change using the formula:

ΔH=MCΔT
if the experiment is exothermic is the energy change negative?

also, my experiment is to do with the displacement reaction between magnesium and copper sulphate. can i draw a graph with the mass of magnesium against the energy change? if so, how do i draw it when the results are negative? wouldnt the graph be odd?shall i just draw a graph where i plot the mass of magnesium against the average temperature difference?
Reply 1
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the_reason
OP
sorry..im just soooo desperate
the_reason
when calculatin the energy change using the formula:

ΔH=MCΔT
if the experiment is exothermic is the energy change negative?

Yes, exothermic is negative. There is actually a minus sign in the formula to accomodate this:
ΔH=-MCΔT

also, my experiment is to do with the displacement reaction between magnesium and copper sulphate. can i draw a graph with the mass of magnesium against the energy change? if so, how do i draw it when the results are negative? wouldnt the graph be odd?shall i just draw a graph where i plot the mass of magnesium against the average temperature difference?

Plotting it against temperature difference or against energy change will give the same graph as they are proportional (but temp. will be positive). It's your choice, either have a negative graph and not have to change the values measured from the graph, or use temperature.
Reply 3
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the_reason
OP
how do i draw a negative graph?
do i just write (-ΔH) as the units so that i dun have to change all the values?
Reply 4
Avatar for Jonatan
Jonatan
13
the_reason
how do i draw a negative graph?
do i just write (-ΔH) as the units so that i dun have to change all the values?


Draw origo in the top left corner, and have the Y axis going downwards.

0---------------------------- x axis
|
|
|
|
|
|
|
Y axis
Reply 5
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the_reason
OP
the experiment i am carrying out is the displacement reaction between copper(II) sulphate and magnesium. more specifically, im investigating the energy change between copper(II) sulphate and zinc.

I already have the results and the energy change worked out. but if the reaction is exothermic, then the energy change is negative. however, there cant be negative energy can there? for drawing the graph do i just plot them with negative energy change?

one more question bfore i go...what can be a possible extension to this experiment? is there any other chemicals i can use? a better method?

has this got anything to do with the 2nd law of thermodynamics?

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