2. A 2 kg rod of aluminum (c = 0.9 kJ/kg-C) at 90C is dropped into 10 L of water at 10C. What is the final temperature of the mixture?
4. A liter of gas, initially at a pressure of 500Pa, is compressed from 1.00 L to 0.25 L. During the compression process, heat is dissipated to maintain a constant temperature. What is the final pressure?
5. A radioisotope thermoelectric generator (RTG) generates electricity by absorbing heat from a core containing a radioactive material (Plutonium 238 is typical) and discharging it into the environment. An RTG installed on an unmanned sonobuoy, tethered to the ocean floor, has a core temperature of 150 C, and discharges heat into sea water at 10 C. What is its theoretical efficiency?
1. Specific heat for H2O is 1 cal/(g.celsius), 1 liter of water is 1000 g.
For water from 20 to 100C, energy needed: 1000*1*(100-20) = 80*10^3 cal = 80 kcal
Heat of Vaporization of Water Hv = 2260 J /g = 2260/4.2 cal/g
For 1000g ...
The expert calculates the energy required to change temperatures.