Thermodynamics. Temperature Particles Pressure, volume and temperature Energy and Power Heat...
Transcript of Thermodynamics. Temperature Particles Pressure, volume and temperature Energy and Power Heat...
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