Chemistry problem, what to do this to make it correct

[Jurrasic]

Calculate, (in J) the change in internal energy for a balloon that is heated by adding 215 cal of heat.?
It expands doing 422 J of work on the atmosphere?
convert everything to J, and use the formula for change in energy:
Energy final - Energy initial
(only problem is if you use that you set it up this way: -422J - (+899.56 J) and that would give a wrong answer wouldn't it?
Because 425 was released and 899.56 was absorbed? So using the equation makes it wrong? You shouldn't subtract your initial energy if it is absorbed, but the equation says to subtract the initial energy? So how do you do this? )

Is 477.56 the correct answer?

 

[danago]

Think about the first law of thermodynamics:

\Delta U = Q + W

i.e. the change in internal energy of a closed system is equal to the heat input into the system plus the work done on the system (you will sometimes see this written as Q - W instead, but in this case W is the work done by the system; they are both correct).

In this case W will be negative, so your answer looks ok to me.

 

[Jurrasic]

Think about the first law of thermodynamics:

\Delta U = Q + W

i.e. the change in internal energy of a closed system is equal to the heat input into the system plus the work done on the system (you will sometimes see this written as Q - W instead, but in this case W is the work done by the system; they are both correct).

In this case W will be negative, so your answer looks ok to me.

helpful answer :) Thank you, it truly helps! :)