Understanding States of Matter and Energy Changes

Posted on Jan 8, 2025 in Physics

States of Matter and Their Properties

Changes of State: When a substance changes its state, its mass is conserved. This is a physical change, meaning it does not produce a new substance. If the changes are reversed, the substance regains its original properties. Evaporation does not have to occur at the boiling temperature of the liquid; it involves only a few particles becoming a gas. In a liquid, particles have a range of energies. At the surface, some particles will have enough energy to escape and overcome the attraction of other liquid particles. This leaves the less energetic particles in the liquid, resulting in a cooler temperature.

  • Gas transforms into a liquid via condensation.
  • Liquid transforms into a solid via freezing/solidifying.
  • Solid transforms into a gas via sublimation.
  • Gas transforms into a solid via deposition.
  • Solid transforms into a liquid via melting.
  • Liquid transforms into a gas via evaporation/boiling.

States of Matter

  • Solid: Particles are closely packed in a fixed position, maintaining a fixed volume and shape. They cannot flow and vibrate against each other.
  • Liquid: Particles are closely packed but can flow past each other. They have no fixed shape but maintain a fixed volume.
  • Gas: Particles are spread far apart and can be compressed. They have no fixed shape or volume.

Specific Heat Capacity

Specific Heat Capacity (SHC) is the amount of heat required to raise the temperature of 1 kg of a substance by 1°C. The formula is: C = ΔE / (m x ΔT), where C is the specific heat capacity, ΔE is the change in energy, m is the mass, and ΔT is the change in temperature. An object with a high SHC takes longer to heat up than a substance with a low SHC.

Specific Heat Capacity Required Practical

  1. Place a beaker on a balance and zero it.
  2. Add oil to the beaker and record the mass of the oil.
  3. Place a thermometer and an immersion heater into the oil.
  4. Read the starting temperature of the oil.
  5. Wrap the beaker in insulating foam to retain as much heat as possible.
  6. Connect a joulemeter and power pack to the immersion heater.
  7. Leave for 30 minutes.
  8. Read the number of joules of energy that passed into the immersion heater and the final temperature of the oil.
  9. Calculate the SHC of the oil using the equation.
  10. Repeat multiple times and calculate an average.

Specific Latent Heat

Specific Latent Heat (SLH) is the energy needed to change the state of 1 kg of a substance. There are two types:

  • SLH of Fusion: Energy needed to melt or freeze 1 kg of a substance.
  • SLH of Vaporization: Energy needed to boil or condense 1 kg of a substance.

The temperature remains constant during a state change because all the energy is used to break the bonds between particles.

Gas Pressure

Molecules of a gas are in constant random motion. The temperature of the gas is related to the energy of the particles; higher energy means higher temperature. When molecules collide with the container’s wall, they exert a force. The total force exerted by all particles on a unit area of the wall is the pressure.

  • Increasing the temperature of a gas at a constant volume increases its pressure.
  • Increasing the volume of a gas at a constant temperature decreases its pressure.

Pressure is calculated as: Pressure = Force / Area (P = F / A). Doing work on a gas involves compressing or expanding it, thus changing its volume. Pumping more gas into the same volume while keeping the temperature constant increases the pressure. Work done is calculated as: Work Done = Pressure x Change in Volume (W = P x ΔV).

Density

Density is defined as mass per unit volume, indicating how closely packed the particles are. Normally, volume is calculated as length x width x height, but measuring the volume of an irregularly shaped solid can be challenging.

Density Required Practical (Eureka Can Method)

  1. Measure the mass of the object using a balance.
  2. Fill a Eureka can with water, just below the spout.
  3. Place the object in the Eureka can and position a measuring cylinder under the spout. Measure the volume of water that comes out.
  4. The volume of water displaced equals the volume of the object.
  5. Calculate the density using the equation: Density = Mass / Volume.

Equations

  • Specific Heat Capacity: C = ΔE / (m x ΔT)
  • Pressure: P = F / A
  • Density: D = M / V
  • Internal Energy: Total Kinetic Energy + Thermal Energy