3. Explain why it was necessary to create the state function we call entropy. Derive the Second Law of Thermodynahics as part of your explanation. 4. Explain what is meant by each of the following terms: system surroundings universe 5. Model the processes of the melting of ice and the freezing of water in the following manner to show that entropy increases for both of these processes. Set up a simplified model with two systems at different temperatures separated by a heat-conducting wall. The volumes of the systems are constant but not necessarily equal. The two systems are isolated from the surroundings. Derive an equation for the entropy dS of the two systems and use it to show that whether ice melts or water freezes, the entropy will increase 6. Explain why, for a reversible prodess, dSrev-0. 7. Calculate the entropy change for the isothermal, reversible expansion of one mole of an ideal gas from 10.0 L to 22.5L