Question

2 mol of solid iron (C = 25.1 J/(mol K)) is heated from 20C to 200C. How much does its internal energy change?

U = q +W but no matter exchange so work is 0. then U=q=9036J
But why is q not negative since isnt the system loses its heat to the surrounding

Answer 1

To heat the iron you are adding heat to it. The iron absorbs heat. That's +.

Answer 2

lets just say that 5g of solid benzoic acid burns under gaseous oxygen atmoshphere. Temperature increases from 20c to 50c. So is this exothermic so the sign is negative?
how is it not the same as above question