Kinetic Molecular Model of Matter and Temperature
KINETIC MOLECULAR MODEL OF MATTER
States of Matter
- They have a fixed shape and volume.
- They have strong forces of attraction between their particles.
- They have a fixed pattern (lattice).
- Their atoms vibrate but cannot change position.
- They have a fixed volume and change shape depending on their container.
- They have weaker attractive forces than solids.
- They do not have a fixed pattern; they take the shape of their container.
- Particles slide past each other.
- They do not have a fixed shape or volume; they fill up containers.
- They have almost no inter-molecular forces.
- Their particles are far apart, and move quickly.
- They collide with each other and bounce in all directions.
Pressure in Gases
- The pressure gases exert on a container is due to the particles colliding on the container walls.
- If the volume is constant, then increasing the temperature will increase the pressure.
Photo Credit: ResearchGate.net
- Gas molecules move randomly.
- This is because of repeated collisions with other gas molecules.
- Small molecules move much faster and have higher energy than larger molecules.
- The small particles can help move the larger particles.
- Brownian motion can be see visually in smoke.
- It is the escape of more energetic particles and occurs constantly on the surface of liquids.
- If more energetic particles escape, liquid contains few high energy particles and more low energy particles, so the average temperature decreases.
- Evaporation can be accelerated by:
- Increasing the Temperature: More particles have energy to escape.
- Increasing the Surface Area: More particles are close to the surface.
- Reducing the Humidity Level in Air: If the air is less humid, fewer particles are condensing.
- Blow Air across the Surface: This removes molecules before they can return to the liquid.
- Pressure Change: P1V1 = P2V2
- Temperature does not measure the amount of thermal energy in a body:
- Two objects of different masses made of the same material at the same temperature would have different amounts of heat.
- When a substance melts or boils, heat is added but there is no temperature energy.
- Thermal energy is transferred from a region of higher temperature to a region of lower temperature.
- Thermal equilibrium is a condition when two or more objects in contact have the same temperature so there is no net flow of energy between them.
NOTE: Not equal internal energy because the number of molecules are unknown.
- Regions of equal temperature are in thermal equilibrium.
- A physical property that varies with temperature may be used for the measurement of temperature. For example:
- Change in volume of a liquid or gas
- Change in pressure of a gas
- Change in electrical resistance
- Change in E.M.F. of a thermo-couple.
- The physical property should have the following qualities:
- The change in property with temperature should be large enough to be measured accurately.
- The value of temperature recorded should be reproducible, i.e. the measured property should be the same when recorded a second time
- The property being used must be suitable over the temperature range being measured.
- It should be able to be calibrated easily, hence the property should change uniformly with temperature.
- Thermodynamic (Kelvin) Scale is a theoretical scale that is independent of properties of any particular substance.
- Based on the idea that the average K.E. of particles of a substance increase with temperature, and the average K.E. is the same for all substances at a particular temperature. K = °C + 273.15
- Absolute zero is the temperature at which a system has minimal internal energy (not zero) – it is impossible to remove any more energy – at 0 Kelvin.
- Triple point of pure water is the temperature at which water exists as a vapor, a liquid, and a solid – at 273.16 K (0.01 °C)