An ideal gas in a frictionless piston–cylinder device doubles its volume while its temperature remains constant because it absorbs heat from an external reservoir. Which statement best describes the signs of q and w for the gas and classifies the overall process?
a) q is positive and w is positive; the process is endothermic.
b) q is zero and w is negative; the process is neither endothermic nor exothermic.
c) q is positive and w is negative; the process is endothermic.
d) q is negative and w is positive; the process is exothermic.