thermal properties and temperature
2.2.1 | thermal expansion of solids, liquids, and gases
thermal expansion
thermal expansion is the increase in volume of a substance when it is heated. all materials expand when heated, but the amount of expansion depends on the material.
uses of thermal expansion
- expansion joints in bridges and railways to prevent damage due to expansion.
- thermometers use the expansion of liquids (like mercury or alcohol) to measure temperature.
- bimetallic strips in thermostats use differential expansion of two metals to control heating systems. (not needed for examination, just another example)
particle arrangement as temperature increases
as temperature increases, particles gain kinetic energy and vibrate more vigorously. in solids, this causes the particles to move further apart, leading to expansion. in liquids and gases, particles move faster and spread out more, also causing expansion.
thermal expansion
as temperature increases, particles gain kinetic energy and vibrate more vigorously, causing them to move further apart and expand
2.2.2 | specific heat capacity
internal energy
internal energy is the total kinetic energy of all the particles in a substance. if the temperature increases, the particles move faster and have more kinetic energy, meaning that they have more internal energy.
specific heat capacity
specific heat capacity is the amount of energy required to raise the temperature of 1 kg of a substance by 1°C.
energy = mass × specific heat capacity × temperature change
E = mcΔθ
experiments to measure specific heat capacity
to measure specific heat capacity, a calorimeter is used to measure the energy transferred to a known mass of substance and the resulting temperature change.
particle arrangement as temperature increases
as temperature increases, particles gain kinetic energy and vibrate more vigorously. in solids, this causes the particles to move further apart, leading to expansion. in liquids and gases, particles move faster and spread out more, also causing expansion.
specific heat capacity
specific heat capacity is the amount of energy required to raise the temperature of 1 kg of a substance by 1°C, defined by the equation E = mcΔθ, where E is energy, m is mass, c is specific heat capacity, and Δθ is the temperature change.
2.2.3 | melting, boiling and evaporation
latent heat
latent heat is the energy required to change the state of a substance without changing its temperature. it is measured in joules (J). the energy in latent heat goes into overcoming the forces of attraction between particles, which is why the temperature remains constant during a phase change.
evaporation
evaporation causes a liquid to cool, as the particles that escape carry greater kinetic energy with them, decreasing the average kinetic energy of the remaining particles, and decreasing the temperature.
factors affecting evaporation
- temperature: higher temperatures increase evaporation rate as more particles have enough energy to escape.
- surface area: larger surface area allows more particles to escape, increasing evaporation rate.
- humidity: lower humidity increases evaporation rate as the air can hold more vapor.
- wind speed: higher wind speeds remove evaporated particles from the surface, increasing evaporation rate.
if an evaporating liquid is kept in contact with an object, the object cools, as the thermal energy is transferred to the object, which is then carried off by the evaporating particles.
evaporation vs boiling
evaporation is the process where particles at the surface of a liquid gain enough energy to escape into the gas phase at temperatures below the boiling point. boiling occurs when a liquid is heated to its boiling point, causing bubbles of vapor to form throughout the liquid and rise to the surface. evaporation is a surface phenomena, as it only happens on the surface, while boiling happens throughout the liquid.
particle arrangement during phase changes
during melting, particles gain enough energy to overcome some forces of attraction, allowing them to move past each other while remaining close together in a liquid state. during boiling, particles gain enough energy to completely overcome forces of attraction, allowing them to move freely and spread out in a gas state.
during condensation, particles lose energy and come closer together, forming a liquid. during solidification/freezing, particles lose energy and come closer together, forming a liquid.