I think the answer in the book is wrong. Problem posed: "In a specific heat experiment 100 gm of lead (cp = 0.0345 cal/gm C) at 100 C is mixed with 200 gm of water a 20 C. Find the difference in entropy of the system at the end from its value before mixing."
I assumed this was an irreversible process, and the key was the final temperature which I calculated at 294.4 K. Following convention, an intermediate reservoir could be put at the final temperature, and the lead would lose so much heat and entropy, the water would gain a little heat and energy, and in the end, the total entropy would increase by 0.20 cal/deg K.
I have calculated final temp a couple ways, with the same answer, but cannot figure out why the answer is what it is. What am I doing wrong, or is the book answer truly incorrect, a rare occurrence?