1. Matter and Energy

2. Drill Answer the following: 1) List the 3 types of energy: 2) The air inside of a basketball left outside on a cold day cools and contracts. Assuming the air is our system, did heat transfer occur? If so, what was the sign?

3. Practice Problem

6. Matter and Energy Energy can go into or out of a system as either work or heat …so far we’ve covered: Thermodynamics - “the study of systems and energy transfer” Work: Mechanical Work = F x d Expansion/Compression Work, Energy, (E): Potential Energy (PE) = m g h Kinetic Energy (KE) = Internal Energy (U) Heat: Heat (Q) } E = PE + KE + U

7. Matter and Energy 1 st Law of Thermodynamics: Thermodynamics - “the study of systems and energy transfer” “Energy can be neither created nor destroyed, only transformed.” “Any change in the energy of a closed system must be caused by either work or heat.” or…

8. Matter and Energy 1 st Law of Thermodynamics: Thermodynamics - “the study of systems and energy transfer” The subscripts “ 1-2 ” should be read as “ 1 to 2 ” and refer to a change in the state of the system from State 1 to State 2. That change in state is a process. State 1 State 2 Adding heat or work to a closed system changes the energy stored in the system; it changes the state of that system. We are now going to investigate some special processes.

9. Matter and Energy Special Types of Processes: Thermodynamics - “the study of systems and energy transfer” Adiabatic – process with no heat transfer (Q=0) Isothermal – constant temperature process Isometric – constant volume process Isobaric – constant pressure process The heat transfer to or from a system can be reduced by surrounding the system with insulation. The gas trapped in this piston-cylinder is now well insulated. Heat Transfer, Q A “well insulated” system can be assumed to be adiabatic. One example of an isobaric process is a vertical piston- cylinder where the piston rests freely on the substance supporting it. The weight of the piston and the pressure of the surroundings are responsible for the pressure inside the cylinder; since neither of these changes, the pressure inside remains constant. If energy is added to the system, the temperature or volume may change, but the pressure will stay the same. Simple, vertical piston-cylinders are isobaric processes. Weight = mg Pressure of Surroundings Heat Transfer, Q Any process that occurs within a “closed, rigid container” is an isometric process.

10. Practice Problem A large, rigid steel tank contains a quantity of water that is heated until it vaporizes. If the heat transferred to the water was 5000 kJ, what was the change in energy of the system?

11. Practice Problem 0.2 kg of air at 100 kPa is trapped beneath a free-floating piston inside of a well insulated, vertical cylinder. If the air is compressed from an initial volume of 1 m 3 to half its original volume, what is the work done? What is the change in energy?

12. Matter and Energy Let’s talk a bit more about pressure… Thermodynamics - “the study of systems and energy transfer” We are all walking around at the bottom of an ocean of air. The weight of all that air above us exerts a pressure on us and everything around us. That pressure is what we call atmospheric pressure, P atm. We often use pressure gauges, P gauge, to measure the pressure of a system if it is above atmospheric pressure. We use vacuum gauges, P vac, to measure the pressure of a system if it is below atmospheric pressure. P atm P = 0 P gauge P vac P abs The absolute pressure, P abs, of a system always references zero pressure. P abs is the pressure that we will use in thermodynamics. P abs

13. Drill Given Pabs = 150 kPa, what would Pgauge be? Given Pabs = 90 kPa, what would Pvac be?

14. Matter and Energy Let’s talk a bit more about pressure… Thermodynamics - “the study of systems and energy transfer” Pressure is sometimes measured with a gauge called a manometer. Tank P atm Pressure increases as you move downwards in a fluid; it decreases as you move up. The pressure at a certain depth within a fluid is the same throughout the fluid at that depth, P 1 =P 2. Pressure changes very little with depth for a gas for small distances, therefore the pressure of a gas in a tank can be assumed to be the same all through the tank. The gauge pressure recorded by the manometer below for the gas in the tank is, P tank = ρ gh. P P tank = P 1 = ρ gh P2P2 P1P1

15. Matter and Energy Before we work an example, let’s discuss how we solve problems… Thermodynamics - “the study of systems and energy transfer” Use the following format: Known: State what is known about the problem Find:State what you are solving for (with units) Sketch:Draw the system Assumptions:List any assumptions necessary to solve Solution:Write out any equations and solve

16. Matter and Energy Thermodynamics - “the study of systems and energy transfer” A mercury manometer is used to measure the pressure of a gas in a tank. The mercury ( ρ = 13,530 kg/m 3 ) is displaced by a height of 0. 05 meter. What is the gage pressure of the gas in the tank? What is the absolute pressure? Tank P atm Known: A mercury manometer measures gas pressure ( ρ = 13,530 kg/m 3 ),h=0. 05 m. Find: Pressure of gas in tank, P tank in Pa; Absolute pressure of gas in tank, P abs in Pa Sketch: Assumptions: P atm = 101.3 kPa, P tank = P 1 Solution: P tank = P 1 = ρgh P tank = ( 13,530 kg/m 3 )(9.8 m/s 2 )(0.0 5 m) P tank = 6630 Pa P abs = P tank + P atm = 6.630 kPa + 101.3 kPa = 107.93 kPa