5.1 | thermal physics

what is temperature?

a number used to indicate the level of hotness of an object on some scale.

what are the fixed points of the celsius scale?

0°C for the melting point of pure ice and 100°C for the boiling point of water under atmospheric pressure.

what is the thermodynamic scale of temperature based on?

the triple point of pure water at 273.16K and absolute zero.

how is temperature in kelvin related to celsius?

T(K) = T(°C) + 273.16.

what happens when two substances at different temperatures are in contact?

there will be a net flow of thermal energy from the hotter object to the cooler object until they reach thermal equilibrium.

what is thermal equilibrium?

a state where there is no net transfer of thermal energy between two objects.

describe the arrangement of atoms in solids.

atoms are closely packed together with strong electrostatic forces of attraction.

what is the kinetic energy behavior of molecules in solids?

molecules vibrate around fixed positions.

how do the molecules in liquids differ from those in solids?

molecules have greater mean separation and more kinetic energy, allowing movement.

what is the electrostatic potential energy in liquids compared to solids?

it is less negative in liquids than in solids.

what characterises the gaseous phase of matter?

molecules have the most kinetic energy, move freely and randomly, and collide elastically.

what is brownian motion?

the random motion of gas molecules, observable through smoke particles in air.

what is internal energy?

the sum of the randomly distributed kinetic and potential energies associated with the atoms or molecules of a substance.

what happens to the kinetic and potential energy of a substance when it is heated but remains in the same state?

the kinetic energy increases while the potential energy remains the same.

what occurs during a phase change in terms of energy?

potential energy increases while kinetic energy remains the same, and temperature stays constant.

what is absolute zero?

the point at 0K where all molecules stop moving and have minimal internal energy.

what is specific heat capacity?

the energy required per unit mass to increase the temperature of a substance by 1K.

what is the equation for specific heat capacity?

E = m * c * ∆θ

what are the units of specific heat capacity?

Jkg⁻¹K⁻¹.

how can specific heat capacity be determined using the method of mixtures?

known masses of substances at different temperatures are mixed until thermal equilibrium is reached.

what happens to the internal energy at absolute zero?

it is entirely due to electrostatic potential energy, as there is no kinetic energy.

what is the role of thermal energy during a phase change?

it is used to overcome electrostatic bonds between molecules.

how can the specific heat capacity of a substance be determined?

by using an electrical heater to heat a known mass of the substance, measuring the initial and final temperatures, and calculating energy transfer.

what is the formula for calculating specific latent heat?

E = mL

what is the specific latent heat of fusion?

the energy required per unit mass to change a substance from solid to liquid.

what is the specific latent heat of vaporisation?

the energy required per unit mass to change a substance from liquid to gas.

how is the specific latent heat determined experimentally?

by heating an object with an electrical heater and monitoring the duration of constant temperature during the phase change.

what is avogadro's constant?

6.02×10^23

how can the number of moles of a substance be calculated?

using the formula n = m/M, where n is the number of moles, m is the mass, and M is the molar mass.

how does the kinetic theory explain gas pressure in a container?

gas pressure is produced by collisions between gas atoms and the walls of the container, with the total pressure being the sum of forces from these collisions divided by the area of the wall.

what is boyle's law?

for a fixed mass of gas at constant temperature, pressure is inversely proportional to volume.

what happens to the temperature of a substance during a phase change?

the temperature remains constant while the substance is changing phase.

what is the role of an insulator in measuring specific heat capacity?

to minimise external energy transfer and increase accuracy in temperature measurements.

what is the unit for specific latent heat?

J/kg

what is the significance of perfectly elastic collisions in gases?

they ensure that the total kinetic energy and momentum are conserved during collisions.

what does the term 'change in momentum' refer to in the context of gas collisions?

it refers to the difference in momentum before and after a collision, calculated as p = m(v-u).

how is the average force exerted by gas atoms on the container wall calculated?

using the formula F = 2mv, where m is the mass of the atom and v is its velocity.

what is the relationship between pressure, force, and area in a gas?

pressure is equal to the total force exerted by gas collisions divided by the area of the wall (P = F/A).

what is the significance of the time taken for atoms to collide in the kinetic theory?

it is negligible compared to the time between collisions, allowing for simplified calculations.

how can the energy transfer during heating be calculated?

by multiplying power (VI) by the time the substance is heated.

what is the effect of increasing the mass of a substance on its specific heat capacity calculation?

it allows for more accurate determination of specific heat capacity when combined with temperature change.

what happens to the energy of a substance when it changes phase?

energy is absorbed or released without a change in temperature.

what does charles' law state about the relationship between volume and temperature for a fixed mass of gas at constant pressure?

the volume is directly proportional to temperature.

what equation represents the relationship among pressure (p), volume (V), temperature (T), and a constant (k) in gas laws?

pV/T = k.

what is the value of the molar gas constant (R)?

8.31 Jmol⁻¹K⁻¹.

what experimental setup can be used to investigate boyle's law?

a sealed syringe filled with gas connected to a pressure gauge.

what should be plotted to demonstrate boyle's law experimentally?

a graph of pressure against 1/volume.

how can absolute zero be estimated using gas pressure and temperature?

by plotting pressure against temperature and finding the x-intercept of the linear graph.

what happens to gas molecules at absolute zero?

they have no kinetic energy, resulting in no collisions with the container walls and therefore no gas pressure.

what is the root mean square speed (r.m.s. speed) of gas molecules?

it is determined by summing the square of all individual velocities, dividing by the number of molecules, and taking the square root.

how is pressure related to root mean square speed in gas molecules?

p = (1/3)Nmc², where N is the number of molecules, m is the mass of a single molecule, and c is the r.m.s. speed.

what does the maxwell-boltzmann distribution illustrate?

it shows the number of molecules with each speed against speed, indicating the spread of molecular speeds in a gas.

how does the maxwell-boltzmann distribution change with increasing temperature?

the peak shifts to a higher speed and the distribution becomes more spread out.

what is the boltzmann constant (k) and how is it calculated?

k = R/NA, where R is the molar gas constant and NA is Avogadro's constant.

how can the equation for an ideal gas be expressed using the number of molecules (N)?

pV = NRT.

what is the relationship between kinetic energy and temperature for gas molecules in an ideal gas?

the kinetic energy is proportional to temperature, measured in kelvin.

what is the equation for mean kinetic energy of gas molecules?

Ek = (3/2)kT.

what is the internal energy of an ideal gas composed of?

the sum of the kinetic and potential energies, but for an ideal gas, it is equal to the kinetic energy since potential energy is negligible.

how is the internal energy of an ideal gas related to temperature?

the internal energy is proportional to temperature.

what is the equation that relates mean kinetic energy to root mean square speed?

(3/2)kT = (1/2)mv².

what does the term 'ideal gas' imply about the interactions between gas molecules?

it assumes there are no electrostatic forces between molecules.

what does the area under the maxwell-boltzmann curve represent?

it represents the total number of molecules.

what is the effect of friction on the accuracy of boyle's law experiments?

friction can produce heat, which should be minimised by lowering the syringe slowly.