1. Forms of Energy: The First Law of Thermodynamics
Chapter 7
Forms of Energy: The First Law of Thermodynamics

2. Section 7.1—Forms of Energy
The total energy of a system is defined as the sum of:
Kinetic energy
Energy due to translational motion
Typically negligible because the operation itself would have to be in motion
Potential energy
Energy due to height or position
Internal energy
Energy contained within the system
e.g. kinetic energy of molecules, vibrational and rotational energy of molecules, etc.

3. Closed Systems
A closed system is one in which no mass is transferred across its boundaries
Energy can therefore be transferred between system and surroundings in two distinct ways:
Heat
Result of a temperature gradient
Defined as positive when transferred to system from the surroundings
Work
Energy transferred in any other manner other than a temperature difference
e.g. a moving piston, torque, voltage, etc.
Defined as positive when it is done by the system on the surroundings

4. Section 7.2—Kinetic and Potential Energy
Kinetic energy is defined as:
Ek = ½ mu2 OR Ek = ½ mu2
Example:
Water is pumped from a storage tank through a tube of 3.00 cm inner diameter at the rate of m3/s. What is the energy flow rate for this stream in J/s?

5. Potential Energy Potential energy is defined as: Ep = mgz OR Ep = mgz
Example
Water is pumped from one reservoir to another 300 ft away. The water level in the second reservoir is 40 ft above the water level of the first reservoir. What is the increase in potential energy of the water in Btu?

6. Energy Balances on Closed Process
In a closed system process, 60 Btu of heat is added to the system, and the internal energy of the system increases by 220 Btu. Calculate the work of the process.
A gas is contained in a cylinder fitted with a movable piston. The initial gas temperature is 25 C. The cylinder is placed in boiling water with the piston held in a fixed position. Heat in the amount of kcal is transferred to the gas, which equilibrates at 100 C (and a higher pressure).
The piston is then released, and the gas does 100 J of work in moving the piston to its new equilibrium position. The final gas temperature is 100 C. Write the energy balance equation for each of the two stages of the process and neglect the change in potential energy of the gas as the piston moves vertically.

7. Section 7.4—Energy Balances on Open Systems at Steady State
For these systems mass is crossing system boundaries at a certain flow rate; therefore, work must be done to accomplish this
Two types of work to be discussed:
Shaft work (work done on a moving part within the system) Ws
Flow work (the net rate of work done at the system outlet and inlet)
Wfl
The work described here is PV (pressure/volume) work

8. Section 7.4c—The Steady-State Open-System Energy Balance
Ultimately relies on the first law of thermodynamics
Input = Output
H + Ek + Ep = Q – Ws
Terms cancel under the same conditions as closed system

9. Section 7.4b—Specific Properties and Enthalpy
Technically a specific property is obtained by dividing an extensive property by the total amount of that property
Ex: heat capacity vs. specific heat capacity
Symbolized by using a  above whatever property is being discussed
Ex: Ĥ or Û
H = m Ĥ

10. Specific Enthalpy and the Open System Energy Balance
One term that occurs in the open system energy balance is change in enthalpy, H
In terms of specific properties: Ĥ = Û + PV
Example: The specific internal energy of helium at 300 K and 1 atm is J/mol, and the specific molar volume at the same temperature and pressure is L/mol. Calculate the specific enthalpy of helium at this temperature and pressure, and the rate at which enthalpy is transported by a stream of helium at 300 K and 1 atm with a molar flow rate of 250 kmol/hr.

11. Section 7.5—Tables of Thermodynamic Data
In the previous example the Û and V were given; however, this is a very unlikely scenario. Most of the times these values will need to be determined using a table of values
Much like using a table to determine G, H, or S
The tables take advantage of the fact that Ĥ and Û are state properties
The tables can be found in Tables B.5 through B.8 in the back of the textbook
All of these values rely on a reference state for their determination
What is the reference state for H values from AP Chem?