Three moles of an ideal gas absorb 2.0kJmol−1 of heat in a certain process. During the same process, the gas performs 900J of work on the surroundings. Determine the change in internal energy of the gas.
(a) 6.9×103J
(b) −5.1×103J
(c) 5.1×103J
(d) 5.7×103J