Chapter 14- Thermal Flashcards
define the triple point of a substance
a specific temperature and pressure where the three phases of matter can exist in thermal equilibrium
what is the net transfer of thermal energy if one object is hotter than another
energy moves from the hotter object to the colder object
what is meant by two objects being in thermal equilibrium
there is no net transfer of energy/at the same temperature
what is the 0th law of thermodynamics
if A is in thermal equilibrium with B
and B is in thermal equilibrium with C
then A is in thermal equilibrium with C
what are the 2 fixed points on the Celsius scale
- 0 is the freezing point of water
- 100 is the boiling point of water
what are the important things about the Kelvin scale
0 is absolute 0
273 is the triple point of water
the increments are the same as in celcius
e.g. 0 celcius = 273 kelvin etc.
what is the kinetic model
it is a model which describes how all substances are made of atoms or molecules arranged differently depending on phase
summarise the particle layout for a solid
- particles are regularly arranged/packed closely
- strong electrostatic forces
- fixed positions
- particles are able to vibrate around their fixed positions so they have KE
summarise the particle layout for a liquid
- particles are very close together but not in a regular arrangement
- particles can flow over each other
- more KE than solids
- weaker electrostatic forces than solids
- random motion of particles
summarise the particle layout for gases
- negligible electrostatic forces
- fast and random motion
- more KE
- collisions between different particles
- collisions between particles and container walls leads to pressure
what is the idea of Brownian motion and how did Einstein explain it
- Brownian motion is the idea that substances were formed of particles and the particles’ KE and collisions determines its motion
- its the idea of random motion
Einstein said:
- collisions between water molecules and pollen grains are elastic
- there is a transfer of momentum from the water molecules to the pollen grains
how can Brownian motion be observed
- set up a light source going through a convex lens
- the light rays should pass through a smoke cell
- a microscope can be placed above the cell, at a right angle
- the smoke particles can be viewed as they scatter the light
- both the smoke particles and the air particles have random motion but only the smoke particles move slow enough to be viewed (they do have the same KE)
what generally happens to density as you change phase
- density decreases from solid to liquid to gas
- this is because the particles have more KE so collide more frequently and take up more room
define the internal energy of a substance
“the sum of the randomly distributed kinetic and potential energies of atoms or molecules within a substance”
what are the two ways that internal energy is increased
increasing temperature, changing phase
why does increasing the temperature of a substance increase the internal energy
the kinetic energies of the particles increases thus the internal energy increases
why does changing phase increase the internal energy of a substance
the potential energies of the molecules increases,
because work is done on the molecules
they are rearranged and electrostatic attraction between them decreases
why do solids and liquids have a negative potential energy
it requires energy to overcome the electrostatic forces between molecules, liquids are less negative than solids
define specific heat capacity
“the specific heat capacity of a substance is the energy required per unit mass (kg) to change the temperature by a unit temperature (1K)”
what is the equation for specific heat capacity
E = mc(delta(theta)) Energy = mass x SHC x change in temp
what tend to be the units for SHC
J kg^-1 K^-1
what is water’s SHC
4.2KJ kg^-1 K^-1
what is the circuit required for the heater when determining SHC and SLH
- a heater in series with a cell, variable resistor and ammeter
- in parallel with a voltmeter
outline the experiment to determine the SHC of a substance
- record the mass of a substance
- fully immerse a heater and place a thermometer into an insulated substance
- record initial temperature
- switch on the heater and start a timer simultaneously
- record the p.d. and current of the heater
- after a set time, stop the timer and record the change in temperature
- given E = VIt,
- C = VIt/m(delta(theta))
