Thermodynamics Thermal Equilibrium Temperature, Study notes of Thermodynamics

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Thermodynamics

Thermal Equilibrium

Temperature

Lana Sheridan

De Anza College

April 17, 2020

Last time

• (^) Torricelli’s Law
• (^) applications of Bernoulli’s equation

HW Problem

A solid sphere of brass (bulk modulus of 14.0 × 1010 N/m^2 ) with a diameter of 3.00 m is thrown into the ocean. By how much does the diameter of the sphere decrease as it sinks to a depth of 1.00 km? (ρseawater = 1030 kg/m^3 )

Introducing Thermodynamics

Now something different. (Chapter 19)

Thermodynamics is the study of temperature, head transfer, phase changes, together with energy and work.

It focuses on relating the bulk properties and behavior of substances. These bulk properties are usually easily measured.

Heat

Heat is a kind of energy transfer into our out of a system.

In the same way we say that something does work on an object, we say that heat flows from one object to another.

Technically, an object does not “contain heat”, heat is just energy being transferred.

The symbol for heat is Q, and units are Joules, J.

Heat

describe the system from the same set of choices. (iii) If the system

the surface, describe the system from the same set of choices.

nergy)

d l, ged f six total total d- s

Work Heat Mechanical waves Matter transfer Electrical transmission Electromagnetic radiation Kinetic energy Potential energy Internal energy System boundary The change in the total amount of energy in the system is equal to the total amount of energy that crosses the boundary of the system. (^1) Figure from Serway & Jewett, 9th ed., page 214.

Temperature

We can go beyond simply saying that two systems are in equilibrium.

We can also compare two systems that are not in equilibrium by analyzing which way heat is transferred when they are brought into contact.

We create a scale for thermodynamic systems to compare them: temperature, T. (^1) Figure: Tom Benson, Glen Research Center, NASA, www.grc.nasa.gov.

Temperature

If two systems, A and B are in thermal equilibrium then their temperatures are equal, TA = TB

If system A transfers heat energy to system B, then

TA > TB

(Or, system A is “hotter” than system B.)

If system B transfers heat energy to system A, then

TA < TB

Measuring Temperature

Devices for measuring temperatures are called thermometers.

All such devices work by employing a substance that changes its properties as it changes temperature.

Measuring Temperature

The most familiar tool for measuring temperature is the mercury thermometer.

As the bulb warms, the mercury expands into a thin capillary tube.

Temperature and Absolute Zero

Air thermometer in use:

(^1) Photos from Washington State LASER org website.

Measuring Temperature

Another way to use a gas to measure temperature is to keep a gas at constant volume as its pressure changes. lightly different value. ge when the tempera - e limited range of tem - r, for example, cannot C, and an alcohol ther- 8 C, the boiling point of rmometer whose read- ermometer, discussed

ometer

cale

pparatus shown in Fig - e variation of pressure ersed in an ice-water top of the mercury in difference between the ressure in the flask at A B The volume of gas in the flask is kept constant by raising or lowering reservoir B to keep the mercury level in column A constant. h Scale 0 Mercury reservoir Flexible hose Bath or environment to be measured P Gas Figure 19.3 A constant-volume gas thermometer measures the pressure of the gas contained in This is a constant-volume gas thermometer. (^1) Diagram from Serway & Jewett, 9th ed.

l

move reservoir B up or down

Measuring Temperature

Different gas samples can have different pressures at the same temperature, and different slopes dPdT.

572 Chapter 19 Temperature

(Fig. 19.5). The

the pressure is re

If we extend

find a remarkab

is 2 273.15 8 C! Th

ture must play. I

2 273.15 8 C as its

is indicated as a

become negative

perature scale is

scale. Therefore,

where T C is the C

Trial 2

Trial 3

Trial 1

P

200

T (!C) " 200 " 100 0 100

For all three trials, the pressure extrapolates to zero at the temperature "273.15!C.

All have the same Figure 19.5 x-intercept, however. Pressure versus

Temperature and Absolute Zero

Robert Boyle (1655) speculated there might be a minimum possible temperature.

Guillaume Amontons (1702) made improvements to the air thermometer.

He noticed that his thermometer would not be able to register temperatures below the value where the air was compressed to (effectively) zero volume.

He proposed this as a zero-point of temperature scales.