Density (ρ) = mass (m) / volume (v)
- Density is how much there is in a given volume.
- Density is measured in kg/m3, although it is sometimes more convenient to measure it in g/cm3, in which case, divide it by 1000 to get Kg.
For example, the density of water is 1g/cm3, this is the same as 0.001kg/cm3
For a regular solid
- Find the volume (volume = width x height x depth) in cm3
- Find the mass
- Divide the mass by the volume
For a liquid
- Find the mass (m) by weighing a dry cylinder (M1), and then with the liquid in it (M2) and then find m = M2 - M1
- Use the cylinder to find the volume- it will be in cm3
- Divide the mass by the volume.
Pressure (p) = Force (F) / Area (A)
- Force is measured in Newtons (N) and Area is measure in Metres2 (m2))
- Pressure is measured in either Pascals (Pa) or in Newtons per metre (N/m2). Remember that 1 Pa = 1 N/m2
- Solid objects exert downwards pressure upon where they stand.
- The smaller the surface area, the greater the pressure.
- In stationary liquids and gases, pressure at any point acts in all directions and increases with the depth of the gas or liquid (as it has the mass of the liquid/gas on top of it, which makes it heavier, and so a greater pressure). A difference in pressure between two places in a fluid will result in a flow of the fluid from the place at higher pressure to the place of lower pressure
Pressure and Depth
Pressure difference (p) = Height (m) x density (kg/m3) x Gravitational field strength* (N/Kg)
*On Earth, this is 10N/Kg
The States of matter
- Molecules in a solid are tightly packed and held in fixed positions by strong forces. The molecules vibrate around their fixed positions. As the solid gets hotter, these vibrations get bigger.
- Molecules in a liquid are closely packed but do not have a regular structure. The forces between the molecules are strong, but the molecules can move randomly. It is a fluid.
- Molecules in a gas are widely spread and in a continuous state of random motion. The forces between the molecules are weak, except during collisions. The molecules move randomly and gases are fluids.
- Brownian studied that pollen grains in water will move around randomly.
- The particles in matter (i.e. molecules) are extremely small and in fluids they are in a continuous state of rapid random motion.
- A gas exerts a pressure on objects, for example, the walls of its container, as a result of continuous collisions between the gas molecule and its container. Each individual collision of many millions of molecules colliding per second will result in a significant pressure.
- The random motion of gas and liquid particles explains why pressure acts in all directions at any point.
- The speed if molecules increases with temperature, so as we heat gases in a rigid container, more energetic collisions with the walls occur more frequently, so the pressure increases.
- The temperature of the gas in Kelvin is proportional to the average kinetic energy of the gas molecules.
The Gas Laws
- The gas laws refer to the behaviour of fixed amounts of gas.
- The following properties of a fixed amount of gas change with respect to one another: volume, pressure and temperature.
- Boyles law= P1 x V1 = P2 x V2
- This law shows that volume is inversely proportional to pressure- if you double the volume of a gas, the pressure halves.
- This law only works if it has a fixed temperature.
- For a fixed amount of gas at a constant volume- P1 / V1 = P2 / V2
- Absolute zero is the lowest temperature you can get because it has a pressure of zero- there are no vibrations whatsoever.
- In degrees Celsius, this is -273C
- In Kelvin, this is 0K
- To convert C to K, add 273
- To convert K to C, subtract 273
This is the end of the topic! Well done!
Drafted by Cherry (Chemistry)