Thermodynamics Flashcards
Define internal energy of a substance
The sum of the random distribution of kinetic energies and potential energies of all atoms in a substance.
When does internal energy change?
When temperature is changed, the kinetic energy of the atoms change.
When the state of the substance is changed, the potential energy of the atoms change.
Define specific heat capacity
The energy required to change the temperature of a unit mass by a unit temperature change.
How do you go from °C to K?
T/k = θ/°C + 273
Why is the specific heat capacity of water useful for a central heating system?
The specific heat capacity of water is 4200Jkg^-1k^-1. For 1kg of water, 4200J of energy is needed to increase the temperature by 1°C. The water can absorb or emit a high value of energy for a small temperature change.
Define thermal equilibrium
When two substances in thermal contact are at the same temperature and there is no further heat flow.
What is the equation for thermal equilibrium?
Heat energy lost by hotter substance = heat energy gained by the colder substance
Define specific latent heat
The energy required to change the state of a unit mass at constant temperature.
Define specific latent heat of fusion
The energy required to change the state of a unit mass from solid to liquid at constant temperature.
Define specific latent heat of vaporisation
The energy required to change the state of a unit mass from liquid to gas at constant temperature.
Define Boyle’s Law
For a fixed mass of gas at constant temperature, pressure is inversely proportional to volume.
Define the Pressure Law
For a fixed mass of gas at constant volume, pressure is directly proportional to absolute temperature.
Define absolute zero
The coldest possible temperature where a substance has minimum internal energy.
Define Charles’ Law
For a fixed mass at constant pressure, volume is directly proportional to absolute temperature.
How many atoms or molecules are in a mole of a substance?
Avogadro’s constant (6.02x10^23)
What does n stand for in PV=nRT
n - number of moles
What is the formula for the mass of a gas?
Mass of a gas = number of moles x mass of 1 mole (molar mass)
What is the mass of one mole also know as?
The molar mass
What is the formula for the number of atoms or molecules in a gas?
Number of atoms of molecules in a gas = number of moles x Avogadro’s constant
What happens to the smoke particles in the Brownian motion experiment?
The smoke particles move randomly and continuously.
The smoke particles constantly change direction and speed.
What are conclusions about air molecules from the Brownian motion experiment?
The air molecules bombard the smoke particles from all sides.
The air molecules move randomly and continuously.
The air molecules are too small to be seen through a microscope.
How does a gas exert a pressure on the walls of a container?
A molecule collides with the walls and rebounds so momentum changes direction. (From Newton’s Second Law) the rate of change of momentum means a force is exerted on the molecule. (From Newton’s Third Law) there is an equal and opposite force in the wall. Pressure = sum of forces on a wall from many molecules / area.
Define internal energy of an ideal gas
The sum of the random distributions of kinetic energies of all molecules in a gas.
What is the PE of gas molecules?
Zero
What is an equation to derive Boyle’s, Charles, and the Pressure laws?
PV/T = constant
