Thermochem Question

[niceshrp]

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If a system does 1300J of work on its surrounding, but its internal energy increases by 700J, system gains or loses energy?

I thought U = Q + W, and that since it did work on surrounding, it would be 700 - 1300 = looses 600 (or since U = Q - W in the sense the -P (V) = Work, and it did work on the surrounding).

However, answer says it gains 2000J? Can anyone help me?

 

[Ssina]

you sure it's not by surrounding instead of on!?

 

[Pisiform]

U = Q +W

(increasing internal energy = + 700) , WD by the system (-1300)

700 = Q + (-1300)

Q = 2000

whenever the work is done by the system (subtract) ... whenever work is done on the system ADD

 

[MedPR]

If a system does 1300J of work on its surrounding, but its internal energy increases by 700J, system gains or loses energy?

I thought U = Q + W, and that since it did work on surrounding, it would be 700 - 1300 = looses 600 (or since U = Q - W in the sense the -P (V) = Work, and it did work on the surrounding).

However, answer says it gains 2000J? Can anyone help me?

U = Q +W

(increasing internal energy = + 1300) , WD by the system (-700)

1300 = Q + (-700)

Q = 1300 + 700

Q = 2000

whenever the work is done by the system (subtract) ... whenever work is done on the system ADD

I'm confused. The question says the work done by the system is 1300 and the increasing energy is +700. Wouldn't that change the sign of Q?

 

[Pisiform]

I'm confused. The question says the work done by the system is 1300 and the increasing energy is +700. Wouldn't that change the sign of Q?

yea i fixed it .... i didnt read it right

 

[Ssina]

Good point, totally over looked the fact that 700 in the change in internal energy!

 

[niceshrp]

ohhh.... yeah thanks for the reply... lol I forgot to put that it was the "heat energy" it was asking for (and which I missed in the question).