Thermodynamics

Thermodynamics

• Temperature• Particles• Pressure, volume and temperature• Energy and Power• Heat transfer• Measuring Temperature• Specific heat capacity• Latent heat

ENERGY

Energy (Joule)

• Energy can be transferred or transformed• kinetic• potential (chemical, electrical, gravitational,

elastic)• radiant (sound, light and other

electromagnetic waves)• internal (heat/thermal energy)

TEMPERATURE

Temperature

The temperature of an object is given by the average kinetic energy of its particles.

2. Measuring temperature

Which thermometers use thermal expansion as their thermodynamic property?

a) liquid in glassb) thermistorc) constant volume gas thermometerd) thermocouple

a) liquid in glass

Temperature Scales

use a thermodynamic propertyscales calibrated at 2 fixed points (often melting

ice and boiling water

INTERNAL ENERGY

Internal Energy

The internal energy of an object is the total kinetic and potential energies of the particles.

U = EK +EP

5. Internal Energy

During a change of state from solid to liquid at the melting point:

a) the temperature of the substance stays the same

b) the internal energy of the substance stays the same

c) the kinetic energy of the particles stays the same

Internal Energy

Internal Energy= potential energy of particles + kinetic energy of particlesU = PE + KE

Heat increases internal energy

a) the temperature of the substance stays the same

andc) the average kinetic energy of

the particles stays the same

Which liquid has more internal energy?

cup of hot tea 80oC

water in swimming pool 25oC

THERMAL EQUILIBRIUM

Temperatureaverage kinetic energy of a particledifferent temperatures heat transferreduntil thermal equilibrium

States of matter

1. Thermal Equilibrium

When two objects are in thermal equilibrium:a) their particles are moving at the same speedb) they each contain the same amount of

internal energyc) the average kinetic energy of the particles in

each object is the same

c) the average kinetic energy of the particles in each object is the

same

Heat transfer

Which ice cube will melt first?

GASES

The Ideal Gas

all collisions between atoms or molecules are perfectly elasticno intermolecular attractive forces

Image: http://kaffee.50webs.com/Science/activities/Chem/Activity.Gas_Laws.PSet1.html

Charles’ Law Charles’ Law: the volume of a gas is proportional to the Kelvin temperature at constant pressure

V = kTV1 = T1

V2 T2

Absolute zero

Absolute zero is the temperature at which the particles of a substance have no kinetic energy. This occurs at -273oC.

Kelvin temperature scale

The Kelvin scale of temperature is defined by absolute zero and is designed so that 1 Kelvin = 1 oC. This gives absolute zero (0K) as -273.15 oC.

Example: Calculate the volume at 75ºC of of a gas sample that at 40ºC occupies a volume of

2.32 dm3

Convert temperatures to Kelvin. 40C = 313K75C = 348K

2.32 dm3 = 313 K V2 348K

(313K)( V2) = (2.32 dm3) (348K)

V2 = 2.58dm3

Heat Transfer

How is heat transferred?

• Conduction• Convection• Radiation

specific heat capacity

How much energy is needed to increase temperature?

Heat capacity

• Describe what happens to the temperature of liquid coffee at 90°C when it is poured into a cup at room temperature.

• Which direction does heat flow?

Image:http://en.wikipedia.org/wiki/Coffee

Heat capacity

• The heat capacity of an object is the energy required to raise its temperature by 1°C

Image: http://en.wikipedia.org/wiki/Milk

Heating waterIt takes 4180J of heat energy to

increase the temperature of 1kg of water by 1°C.

a) how much heat is needed for 0.5kg by 1°C?

b) how much heat is needed for 1kg from 20 to 50C?

c) how much heat for 5kg from 20 to 100C?

specific heat capacity

Heat energy = mass of × specific heat × temperature substance capacity change

E = m × c × ∆T(J) (kg) (J/kg/°C) (°C)

The specific heat capacity is the amount of heat needed to raise the temperature of a mass of one kilogram of a substance by 1 degree Celcius.

Coffee example

6. Specific Heat Capacity

Specific heat capacity of water is 4180J/kg/KThis means 4180J of energy is needed toa) increase the temperature of 10g of water from

20 to 30Cb) increase the temperature of 1 litre of water

from 20 to 21Cc) increase the temperature of 0.1kg of water

from 40 to 50C

b) increase the temperature of 1 litre of water from 20 to 21C

and

c) increase the temperature of 0.1kg of water from 40 to 50C

Specific Heat Capacity

E = mcΔT

shc found from 'the electrical method' or 'the method of mixtures'.

Latent heat

Latent Heat

Latent heat of fusion: energy needed to melt a solid without a temperature rise

Latent heat of vaporization: energy needed to boil a liquid without a temperature rise.

Energy = mass × spedific latent heatE = mL

Ideal gases

3. Temperature and Pressure

The temperature of an ideal gas (in Kelvin) is proportional to its pressure so

a) at absolute zero the pressure is zerob) at absolute zero the particles have no kinetic

energyc) below absolute zero the pressure is negative

a) at absolute zero the pressure is zero

and

b) at absolute zero the particles have no kinetic

energy

Pressure

Gas pressure due to collisions of gas particles with container walls.

Higher temperature > more collisions, more KEUnit of pressure: Pascal 1 Pa = 1 N/m2

4. Pressure, Volume and Temperature

When the pressure of an ideal gas is doubleda) the volume is half if the temperature is kept

constantb) the volume is double if the temperature is

kept constantc) the temperature is double if the volume is

kept constant

a) the volume is half if the temperature is kept

constant

and

c) the temperature is double if the volume is kept

constant

Pressure, Volume and Temperature

P1V1 = P2V2 for a fixed mass of gas

T1 T2