Thermal Physics M.5 Flashcards
Define thermal equilibrium
its when two objects which are in contact are at the same temperature and so there is no net energy transfer between them
What properties does the Celcius scale depend on?
the freezing and boiling points of water
What do we call the lowest temperature possible?
Absolute zero ( 0 K)
What occurs to particles at absolute zero?
they have the minimum possible energy
How do you change a temperature value in degrees Celcius into kelvins?
You add 273
T ( K ) ≈ θ ( ºC) + 273
Describe the arrangement of particles within a solid
- particles vibrate in fixed positions in regular lattice
- particles held together by strong forces of attraction
Describe the arrangement of particles within a liquid
- particles are constantly moving around
- free to move around eachother but are attracted to one another
Describe the arrangement of particles within a gas
- particles are free to move around randomly
- no forces of attraction between them
What is Brownian motion
the random movement of small visible particles suspended in a fluid due to collisions with smaller, randomly moving atoms/molecules of the fluid
How can you observe brownian motion in a lab?
- Put smoke in brightly illuminated glass jar and observe particles using a microscope
- the smoke particles will appear as bright specks moving haphazardly from side to side , and up and down
Define Internal energy
the internal energy of a system is the sum of the random distribution of kinetic and potential energies of its atoms and molecules
What occurs to a substance when you heat it?
its temperature increases →thereby increasing the kinetic energy of particles within it → and so its internal energy increases
What occurs to a substance when it changes phase?
its internal energy changes because the change of phase alters the bonds and therefore the potential energy of the particles
*there is no change in temp when there is a change of phase
Define specific heat capacity
the specific heat capacity of a substance is the energy required to raise the temperature of 1 kg of a substance by 1°C
State the equation for specific heat capacity
E=mcθ
E- the energy change (J)
m - mass (kg)
c- specific heat capacity (J kg¯¹ K¯¹ OR J kg¯¹ °C¯¹)
Explain how you would determine that value of the specific heat capacity of a material
- insulate the material being heated and use lids for liquids to reduce energy losses to the surroundings
- use an ammeter to obtain the values for the current flowing in the circuit, a voltmeter for the pd across the heater and a stopclock to measure the time you’ve spent heating the materials then you can calculate the energy (E) ( E= VIt )
- You then plug in your values into E=mcθ to calculate c
triple point of water
the point at which water can exist as a solid , liquid and gas simultaneously
Temperature
a measure of how hot or cold an object is and is re;ated to the kinetic energy of the particles in a substance
Define specific latent heat
the energy required to change the state of 1 kg of a substance
State the equation for specific latent heat
E=mL
E- energy change (J)
m - mass (kg)
L- specific latent heat ( J kg¯¹)
Explain how you would determine the specific latent heat of a material
For a solid,e.g. ice :
- Place a heater and equal masses of ice in two funnels above beakers
- Turn on one heater for 3 minutes and record the energy transferred (E=VIt) during the 3 minutes. Dont turn the other heater- its there so that you can measure how much ice melts due to the ambient temperature of the room
- After 3 minutes measure the mass of water collected in each beaker then subtract one from the other to get the amount that melted solely due to the presense of the heater
- E=ml and plug in your values to get L
For a liquid
boil water in a distiling flask , condense the vapour given off and divide the energy transferred by the mass of the condensed water collected
Explain the concept , ‘1 mole of substance’
1 mole of a substance contains 6.02x10²³ particles
(this number is known as the Avogadro constant , N**A)
E.g. one water molecule is composed of two hydrogren atoms and one oyxgen atom
hydrogren has an atomic mass of 1 and oxygen has an atomic mass of 16 therefore the mass of one mole of water will be 18g
State the equation to find the number of particles present in a substance
N=nNA
N-no. of particles
n- the no. of moles
NA- Avogadro’s number
1 mole of a substance will contain N**A particles
n moles of a substance will contain nN**A particles
Ideal gas
a gas that has internal energy only in the form of random kinetic energy
State 3 assumptions of the kinetic model of gas
- the particles move rapidly and randomly
- there are negligible forces between particles except during collisions
- all collisions are perfectly elastic ( kinetic energy is conserved)
Pressure
the force acting perpendicular to an area
mean square speed
mean value of the square of the velocity for a large no. of particles moving randomly in a gas
root mean square (r.m.s) speed
its the square root of the mean square speed
State what each variable in the equation of pV=1/3Nmc² represents
p= pressure (Pa or Nm¯²)
V- volume (m³)
N- number of particles
m- mass (kg)
c²- mean square speed
