What is the change in the internal energy of a system that does 400 joules of work and absorbs 700 joules of heat?

When a system uses up 400 J (or does 400 J of work), this means the internal energy decreases by 400 J. When it absorbs 700 J of heat, it means 700 J is added to total internal energy present.

Thus, we have a total change of - 400 + 700 = 300 J in the internal energy of the system.

Answer: 300 J

The formula for finding change in internal energy is: E = q + w, where E equals to change in internal energy, q equals to the amount of heat involved in the reaction and w equals to work done. From the question given, w = 400 and q = 700.

E = 400 + 700 = 1100. Therefore, the change in internal energy is 1,100.