thermal save my exams Flashcards
what is meant by the internal energy of a substance
- the sum of the randomly distributed kinetic and potential energies of the particles in a body
what is meant by randomly distributed?
- they all have different speeds and seperations
what is the internal energy of a system determined by?
- temperature
- random motion of molecules
- phase of matter
- intermolecular interactions between the particles
how can the internal energy of a system be increased ?
- doing work on it
- adding thermal energy to it
how can the internal energy of a system be decreased?
- losing thermal energy to its surroundings
- system doing work on its surroundings
what is the first law of thermodynamics?
- the internal energy of a system is increased when thermal energy is transferred to it or when work is done on it
what happens when a gas expands?
- volume increases
- work is done BY the gas ON the surroundings
- this decreases internal energy
what happens when a gas is compressed?
- volume decreases
- work is done ON the gas BY the surroundings
- this increases internal energy
what happens when a piston moves down?
assume insulated
- space occupied by the gas molecules is compressed
- work is transferred to the systems internal energy
- increasing internal energy of the gas
what happens when a piston moves up?
- space occupied by the gas molecules expands
- work is transferred from the systems internal energy
- decreases internal energy of the gas
what is specific heat capacity of a substance?
- the amount of thermal energy required to raise the temperature of 1kg of a substance by 1K/1*C without changing its state
what are two deductions we can make from specific heat capacity?
- the heavier the material the more energy required to raise its temperature
- the larger change in temperature, the higher thermal energy required
how can thermal energy be calculated?
^Q = mc^T
^Q = change in thermal energy ( J )
m = mass of the substance you are heating
c = specific heat capscity of the substance
^T = change in temperature
what is latent heat capacity?
- the thermal energy required to change the state of 1kg of a substance without changing its temperature
what is the specific latent heat of fusion?
- the thermal energy required to convert 1kg of a solid to liquid with no change in temperature
what is the specific latent heat of vaporisation?
- the thermal energy required to convert 1kg of a liquid to gas with no change in temperature
what is the equation to calculate the energy required to melt/vaporise a mass m
Q = m L
Q = thermal energy
m = mass
L = specific latent heat of fusion / vaporisation
why is the latent heat of vaporisation much greather than the latent heat of fusion?
- more energy has to be supplied to seperate molecules, thank break a solid bond
- intermolecular forces are important
what happens at thermal equilibrium?
- both have same final temperature
what happens when a substance is heated?
- molecules are given energy in the form of kinetic and potential energy
what happens during a change of state?
- no change in temperature
- potential energies of molecules change, but not kinetic energies
why do molecules have potential energies?
- due to their seperation of intermolecular bonds, moving further apart of closer together.
what is absolute zero?
- the temperature at which the molecules in a substance have zero kinetic energy
how do you convert to K and vice versa
• + 273 = K
• = K - 273
what is Boyle’s Law?
- if temperature is constant
pressure is inversely proportional to volume
p1v1 = p2v2
what is Charles Law?
- if pressure is constant
volume is directly proportional to temperature
v1/t1 = v2/t2
what is the Pressure Law?
- if volume is constant
pressure is directly proportional to temperature
p1/t1 = p2/t2
what do ideal gases obey?
pV directly proportional to temperature
why does higher temp lead to higher pressure?
- temperature is a measure of the average kinetic energies of molecules ( speed )
- higher temperatures cause higher speeds, hence molecules collide with the surface of the wall more frequently
- faster the molecules, greater the force due to momentum
pressure increases as P = force per unit area
what can we assume with ideal gas equations?
- collisions are elastic
- has molecules with negligible volume
- obeys Gas laws
- has no interactions between the molecules
