Thermal - 5

• T(K) = T(°C) + 273
• Two objects are in thermal equilibrium when there is no net transfer of thermal energy between them.
• In solids, atoms are closely packed together. There are strong electrostatic forces of attraction between molecules. The molecules have kinetic energy, which allows them to vibrate around their fixed positions.
• In the liquid phase, the molecules are still have a greater mean separation than in solids, but are still close together. They have more kinetic energy, so they can move around
• In gases, the molecules have the most kinetic energy, allowing them to move freely and rapidly, and collide elastically with each other. These collisions result in the molecules traveling with random speed and direction.
• Brownian motion - The molecules of a gas travel in random directions with random velocity.
• The internal energy of a substance is defined as the sum of the randomly distributed kinetic and potential energies.
• When a substance changes state, the potential energy increases, but the kinetic energy and temperature remain the same. as the thermal energy is being used to overcome electrostatic bonds between molecules.
• Absolute zero is 0K, and is the point where all molecules in a substance stop moving completely.
• The specific heat capacity, c of a substance is defined as the energy required per unit mass to increase the temperature by 1K.
• The specific latent heat of fusion is the energy required per unit mass to change the phase of a substance from solid to liquid. The specific latent heat of vaporization is the energy required to change the phase of a substance from liquid to gas.
• The kinetic theory of gases is a model which can be used to describe how particles within in ideal gas behave:

  • The gas contains a large number of atoms that move with random, rapid motion.

  • The volume of the gas atoms is negligible compared to the total volume of the gas.

  • All collisions of atoms are perfectly elastic.

  • The time taken for atoms to collide is negligible compared to the time between collisions.

  • The electrostatic forces between atoms are negligible, except for when the atoms are colliding.
• Boyle’s law - for a fixed mass of gas at a constant temperature, the pressure is inversely proportional to the volume.
• Charles’ law - a fixed mass of gas at a constant volume, the pressure is proportional to temperature.
• The pressure exerted by a gas, and the mean kinetic energy of molecules in the gas, are related to the root mean square (r.m.s.) speed of the molecules.
• The Maxwell Boltzmann distribution shows the number of molecules with each speed, against speed c. As the temperature of the gas increases, the peak of the graph shifts to a higher speed, and the distribution becomes more spread out.
• The Boltzmann constant (k) = molar gas constant (R) / Avogadro’s Constant
• When a molecule collides with a wall elastically, the momentum changes from +mv to -mv so the total change in momentum is 2mv for one particle
• Root mean square speed of the molecules in a gas is the square root of the average speed of the molecules and is used to find the pressure of a gas using the equation pV = 1/3Nm*root(c^2)