1 Why is it incorrect to say that a system contains heat 2 I

1) Why is it incorrect to say that a system contains heat?

2) If you are given the temperature and specific volume of a two-phase, liquid-vapor mixture, describe the process of how you could determine the specific internal energy.

3) If a substance experiences a constant-pressure expansion, at a pressure higher than its critical pressure, will it change phase? If your answer is yes, describe what phases are involved and what change takes place.

4) Calculate the diameter of a pipe carrying water at 20°C and moving at 25 m/s if its mass flow rate is 150 kg/s.

Solution

Ans 1. It is incorrect to say that a system contains heat because heat is a kind of energy flow which takes place due to the difference in temperature and hence we can say that heat is not an internal property of matter i.e. it is just a medium to change the temperature of a system i.e. causes flow of energy and system / matter do only contains internal energy.

Ans 2. You will have to follow a certain steps in order to calculate the internal energy. i am mentioning here stepwise.

Ans 3. If the given pressure is higher than critical pressure of the given substance than there will be no phase change. In case of pure sustance it will resemble a vapour but it is highly unpredictable to say where the phase change is to take place i.e. above the critical state there is no line defined which will  separate the compressed liquid state and the superheated vapor state.