What is temperature? Start with some definitions

Transcription

1 Thermodynamics "Thermodynamics is a funny subject. The first time you go through it, you don't understand it at all. The second time you go through it, you think you understand it, except for one or two small points. The third time you go through it, you know you don't understand it, but by then you are so used to it, it doesn't bother you any more." Arnold Sommerfield

2 What is temperature? Eureka!%20-%20Measuring%20Temperature Start with some definitions

3 Start with some definitions Heat vs. Temperature Eureka!%20Episode%2021%20-%20Temperature%20vs. %20Heat

4 Which has a higher temperature, the bonfire or the match? Which has more heat, the bonfire or the match?

5 Which has a higher temperature, an ice cube or an iceberg? Which has more heat, an ice cube or an iceberg?

6 Energy Is the capacity to do work or cause change. Work is done when an object is moved in the direction in which Work a is force done when is applied. an object is moved in the direction in which a force is form of energy based on moving an object over a distance Other Forms of Energy chemical, electrical, mechanical light (radiant) sound, magnetic

7 Potential & Kinetic Energy Potential Energy Stored energy that an object has by virtue of its position or composition. Kinetic Energy Energy of motion or Energy of a reaction

8 1. The movement of water from the ground through the trunk to the upper limbs of a tree is an important biological process. A. What part of the system if any, undergoes a change in potential energy? B. Is work done in the process? The water changes position --against the force of gravity so it s potential energy has changed. Work is movement of a mass over a distance against an opposing force. The tree does work in lifting the water to its upper limbs

9 2. Which of the following involves the larger change in potential energy? A. a 50 kg object is dropped to the ground from a height of 8m? B. a 20 kg object is lifted from the ground to a height of 20 m? PE = mgh A. Magnitude of PE = (50 kg)(9.8 m/s 2 )(8m) = 3920 J ---> 4000 J B. Magnitude of PE = (20 kg)(9.8 m/s 2 )(20m) = 3920 J-----> 4000J Difference is the direction (sign) of the change. in A the sign is negative in B the sign is positive

10 3. A bowler lifts a 5.4 kg (12 lb)bowling ball from ground level to a height of 1.6 m (5.2 feet) and then drops the ball back to the ground. A. What happens to the potential energy of the bowling ball as it is raised from the ground? The ball is raised to a greater height above the ground--therefore its PE INCREASES

11 3. A bowler lifts a 5.4 kg (12 lb)bowling ball from ground level to a height of 1.6 m (5.2 feet) and then drops the ball back to the ground. B. What quantity of work in J is used to raise the ball? WORK = FORCE X DISTANCE FORCE = MASS X ACCELERATION WORK = MASS X ACCELERATION X DISTANCE W = 5.4 kg x 1.6 m x 9.8 m/s 2 W = J W = 85 J

12 3. A bowler lifts a 5.4 kg (12 lb)bowling ball from ground level to a height of 1.6 m (5.2 feet) and then drops the ball back to the ground. C. After the ball is dropped, it gains kinetic energy. If we assume that all of the work in part B is converted to KE at the point of impact with the ground, what is the speed of the ball at the point of impact? KE= 1/2 mv 2 v 2 = 2KE/m PE is converted to KE so KE = 85J v 2 = 2 (85J)/ 5.4 m v 2 = m 2 /s 2 v = 5.6 m/s

13 4. What is the kinetic energy in J of an Argon atom moving with a speed of 650 m/s? a mole of Argon atoms moving with a speed of 650 m/s? KE= 1/2 mv 2 KE = 1/2 ( 6.63 x g)(650m/s) 2 KE = 1.4 x J KE = 1/2 (39.9g ) (650 m/s) 2 KE = 8.4 x 10 3 J

14 5. Calculate the velocity of an electron whose mass is x g and whose kinetic energy is x J KE = 1/2 mv 2 V 2 = 2KE/m V 2 = 2 (1.585 x J)/9.107 x kg) V 2 = x m 2 /s 2 V = x 10 6 m/s

15 Chapter 6 26, 30, 32, 37, 41, 43, 45, 55, 59, 63, 71, 77, 79

16 FIRST LAW OF THERMODYNAMICS Energy can be neither created nor destroyed. Energy is conserved INTERNAL ENERGY OF A SYSTEM sum of all the KE and PE of all the components of the system. Internal energy is represented with the symbol E Usually we don t know the actual value of E We hope to know the change in the E

17 FIRST LAW OF THERMODYNAMICS Change in E = E final - E initial We don t need the actual values for E final and Einitial only need the value for Δ E Δ E has three components a number a unit a sign

18 When Δ E is positive it indicates E final is greater than E initial Indicates that the system gained energy from the surroundings When Δ E is negative it indicates E final is less than E initial Indicates that the system lost energy to the surroundings

19 Initial state = reactants Final state = products