The 1st Law of Thermodynamics Warm-up State the law of conservation of energy as stated in the textbook (Chapter 8), Describe how heat engines work

answer The law of conservation of energy states that; In a closed system (isolated system), energy can neither be created nor destroyed. Energy can change form but it is always conserved.

2. heat engine:( steam-powered trains) In a heat engine, an input of heat causes an increase in the temperature of the working substance (water), At high temperature, gaseous water (steam) pushes a piston (perform work), which causes the wheel to turn.

question Looking at the heat engine in the previous slide, how would you figure out the amount of work done to turn the wheel?

solution

Problem 100 Joules of heat are added to a drier to dry the clothes. If the exhaust heat is about 40 Joules, how much heat energy was used to dry the clothes? Solution:

First law of thermodynamics This law states that: “Whenever heat is added to a system, it transform to an equal amount of some other form of energy” More specifically, this means:

1st Law of thermodynamics ∆U = Q + W(on the system) ∆U = Q - W(by the system) Where; ∆U – change in internal energy of system Q –Quantity of internal energy of a system W- work done

Heat added External work done Increase in internal energy

Questions If 10 J of energy is added to a system that does no external work, how much will the change in internal energy be? 1000 joules of heat are added to a system consisting of a gas in a cylinder with movable piston top. If the internal energy of the system increases by 700 joules, the work done by the gas on the pistons is: ________________

Class work Textbook page 368 # 1-7

Second Law of Thermodynamics Warm-up How much heat is lost to the environment in calories from 400 g water that cools from 40oC to 23oC. (specific heat capacity of water is 1c/goC) If 10J of energy is added to a system that does 4J of external work, by how much will the internal energy of that system be raised?

solution 1. Heat lost (Q calories) = M •c •∆T = 400g •1c/goC •17oC 2.

Second Law of Thermodynamics The second law of thermodynamics states that: Heat flows from hot to cold objects. Heat will not of itself flow from cold to hot objects. And; Whenever energy transforms, it degenerates into waste. Organized energy (concentrated and therefore Usable energy) degenerates into disorganized energy (non usable energy)

Second law explained. usable is organized. After work, the energy released is disorganized and unusable. The unusable energy becomes air pollution which is waste.

Order tends to disorder Natural systems tend to proceed toward a state of greater disorder.

question A C B Nitrogen molecules within a glass tube are allowed to move randomly. Which figure shows the molecules in a state of greatest entropy?

Order tend to disorder

Entropy Entropy is the measure of the amount of disorder. The second law of thermodynamics says that the total entropy of the universe can never decrease. Organized structure always become disorganized messes over time.

Entropy Organized structure always become disorganized messes.

Class work/Homework Textbook pg 369 # 19-25