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
To heat the iron you are adding heat to it. The iron absorbs heat. That's +.
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
In this case, the change in internal energy (ΔU) can be calculated using the formula ΔU = q + w, where q represents the heat transferred to or from the system and w represents the work done on or by the system.
Since there is no mention of any work being done on or by the system, the work term (w) can be assumed to be zero in this case. Therefore, the equation simplifies to ΔU = q.
Now, to determine the sign of q, we need to consider the direction of heat transfer. In this scenario, the solid iron is being heated from 20°C to 200°C. Since the temperature is increasing, it means that heat is being added to the iron.
For the purposes of calculations, it is common to consider heat being added to the system as a positive value. Therefore, q would also be positive in this case, indicating an increase in internal energy.
So, the change in internal energy (ΔU) is equal to the amount of heat added to the system, which is 9036 J. And since q is positive, the internal energy of the system increases by 9036 J.