Solids Liquids and Gases

• Density

  Density(kg/m*3) = mass per unit volume

  Density = mass/ volume
• Finding the Density of a Liquid

  Finding the Density of a irregular Solid

  Liquid- Measure volume in a measuring cylinder avoid parallax error read straight on. Then measure mass on a mass balance and avoid zero error

  Solid- Measure mass. Place it in a Eureka can fully immerse it and measure the amount of displaced water and this is the volume of the solid
• Pressure

  Pressure ( Pascals, Pa) = force per unit area
• How does Pressure act in Gases and Liquids (2)

  Pressure rests equally in all direction in a gas or liquid

  Pressure in a fluid is created from the movement of particles as they collide with the surface
• How does Pressure act beneath a liquid surface (3)+Equation

  Pressure beneath a surface increases with depth , the density of the liquid and the gravitational field

  Given by p=pgh

  Depth : the deeper the fluid the more particles above the point hence there greater weight

  Density: Fluids with more density have more particles per unit volume therefore greater weight

  Gravitational field: Weight is dependent on Gravitational field
• Effects of heating a system

  Heating a system causes internal energy to rise leading to an increase in temperature or a change of state

  When the temperature of a body rises energy goes towards making the molecules vibrate more and this increases their kinetic energy

  When a body changes state energy goes towards making the molecules freer from each other rather then increasing kinetic energy meaning Temperature stays constant
• Melting and Boiling and Evaporation

  Melting: occurs when molecules in a solid vibrate enough to move away from there fixed positions

  Boiling: When molecules in a liquid gain enough energy to break their bonds and become separate molecules into a Gas

  Evaporation: The escape of molecules with higher energy from surfaces of liquids , after they leave the left over molecules have a lower average kinetic energy( temperature is lower)
• Why is evaporation useful

  Evaporation cools down a liquid , useful for cooling things down like sweating
• Increasing rate of evaporation:

  • Increase temperature
  • Increase surface area
  • Provide a draught (current of cool air)
• Difference between evaporation and Boiling :

  Evaporation can occur at any temperature and only at the surface
• Rule of temperature when changing state

  No change in temperature when there is a change of state because energy is supplied to separating particles
• Structure of:

  Solids:

  Liquids:

  Gases:

  Solids:

  • Tightly packed in regular patterns
  • Strong intermolecular forces of attraction
  • Molecules vibrate but can't move around

  Liquids:

  • Molecules close together in random arrangement
  • Weaker forces of attraction
  • Molecules move around each other Gases :
  • Far apart random arrangement
  • Very weak
  • Move quickly in random/ all directions
• Specific Heat Capacity

  Definition

  Equation

  The amount of energy required to raise the temperature of 1kg of a substance by 1 degree Celsius

  Change in thermal energy= mass x specific heat capacity x change in temperature
• Ideal Gases

  How gas molecules work

  1. Gas molecules move rapidly and randomly due to collisions with other gas molecules
  2. Gas exerts pressure on a container due to collisions between gas molecules and the wall
  3. When molecules rebound of a wall there velocity changes because direction changes therefore there momentum changes
  4. Leading to a force being exerted because Force = change in momentum/ time
• What happens when volume is constant In ideal gases and temperature rises

  If temperature increases so does pressure because :

  Molecules move faster and collide harder and more frequently with walls
• What happens when Pressure =0

  When pressure is equal to zero the temperature is at absolute 0 (-273 Celsius)
• Kelvin scale

  Gasses at fixed mass and volume

  Kelvin scale: Temperature in Kelvin= Temperature in degrees + 273

  Gasses at fixed mass and volume :

  Pressure / Temperature = Constant

  P1/T1=P2/T2
• Ideal Gases at a constant temperature

  If volume increases

  If volume increases , pressure decreases because:

  Molecules collide less frequently over a larger area
• Gases at fixed mass and temperatures (equation) Boyles law

  Pressure x Volume = constant

  P1 x V1 = P2 x V2
• What is temperature is Kelvin directly proportional too

  Temperature in kelvin is directly proportional to average kinetic energy of the molecules

  Higher temperature means higher average kinetic energy and so the average speed of molecules is faster