2.1

## Hanyang University

Skip to 0 minutes and 17 secondsThis week in thermodynamics in energy engineering, we are still talking about the first law of thermodynamics, but we are going be looking at its application to real problem. We encounter situations to calculate energy difference between two states to get some useful information. Let’s take an example. To cool down the warm water at 50 C, we decided to put ice into it. To get a final temperature of 4 C, what might be the amount of ice? Then, we need to calculate the energy flow from the warm water to the ice to melt it down and to make the final liquid mixture at 4 C.

Skip to 0 minutes and 57 secondsWe have to calculate the energy output from the warm water and the energy input to the ice. This week, we are going to solve this kind of problems. For convenience in calculation, people defined a reference state and assign zero enthalpy to it. It gets easier to calculate the enthalpy change in the process with the concept of reference states. From there, we are going to be looking at the enthalpy changes in chemical reactions. Then we are going to move on to the equation of states. The equation of state relates physical variables that describe the condition of materials such as temperature, pressure, volume and quantity.

Skip to 1 minute and 38 secondsWith the help of the equation of states, we can easily convert the dependence of thermodynamic quantities on the temperature into the dependence on other variables.