Solids, Liquids and Gases Flashcards
what is the definition of density?
the mass per unit volume
what is density measured in?
kilograms per metre cubed (kg/m3)
method to find the density of a liquid
- find the mass of the measuring cylinder by placing it on a balance, then fill it with the liquid and measured the new mass - the difference in masses is the mass of the liquid minus the cylinder; this avoids zero error
- the volume can be read from the cylinder and it must be read straight on to avoid parallax error
- find the density using the equation
method to find density of a solid
- measured the mass of the solid by placing it on a balance
- if the solid is regularly shaped, measure its dimensions using a ruler or other measuring tool and then use a mathematical formula to find the volume
- if the solid is irregularly shaped, immerse it in water and measure the volume of the water displaced - this is the volume of the solid
- find the density using the equation
what is the definition of pressure?
the force per unit area
what is pressured measured in?
pascals (Pa)
the greater the area of an object…
the lower the pressure
how does the pressure in a gas or liquid at rest act?
it acts equally in all directions and causes a force at right angles to any surfaces
how pressure is a gas or liquid created?
from the movement of particles as they collide with a surface
how does the pressure beneath a liquid surface increase?
with depth, the density of the liquid and the gravitational field strength
- deeper in the fluid the more particles above the point, hence the greater their weight
- fluids with higher density have more particles per unit of volume, hence greater their weight
what does weight depend on?
gravitational field strength
how does heating a system cause a change of state?
it increases its internal energy and causes either an increase in temperature or a change of state
what happens when the temperature of a body rises?
the energy goes towards making the molecules vibrate more and increases their kinetic energy
what happens when a body changes state?
energy goes towards making the molecules freer from each other rather than increasing their kinetic energy so the temperature stays constant
when does melting occur?
when molecules in a solid vibrate enough to move away from their fixed positions, turning into a liquid
when does boiling occur?
when molecules in a liquid gain enough energy to break their bonds and become separate molecules, turning into a gas
why is there no change in temperature while a substance is changing state?
because energy supplied is used to separate the particles, breaking the forces between the molecules
what is evaporation?
the escape of molecules with higher energy from the surfaces of liquids
why is evaporation useful for cooling things down such as sweating from the body?
after the molecules escape, the remaining molecules have a lower average kinetic energy which means the temperature is lower (evaporation cools the liquid)
how do you increase the rate of evaporation?
- increase the temperature
- increase the surface area
- provide a draught
why is evaporation different to boiling?
it can happen at any temperature and only occurs at the surface of the liquid, whereas boiling occurs throughout a liquid and only at the boiling point
arrangement of particles in a solid
- molecules close together in regular pattern
- strong intermolecular forces of attraction
- molecules vibrate but can’t move about
arrangement of particles in a liquid
- molecules close together in random arrangement
- weaker intermolecular forces of attraction than solids
- molecules move around each other
arrangement of particles in a gas
- molecules far apart in a random arrangement
- very weak intermolecular forces
- molecules move quickly in all directions
what is the specific heat capacity?
the amount of energy required to raise the temperature of 1kg of a substance by 1 degrees celcius
what is specific heat capacity measured in?
joules per kilogram degree celcius (J/kg degrees celcius)
how do gas molecules move?
rapidly and randomly due to collisions with other gas molecules
how do gases exert pressure on a container?
- due to collisions between gas molecules and the wall
- when the molecules rebound off the walls, they change direction so their velocity and therefore their momentum changes
- this means they exert a force equal to the change in momentum over time
why does pressure increase if temperature increases at a constant volume?
because the molecules move faster so they collide harder and more frequently with the walls
what is absolute zero?
the temperature at which the pressure is zero (-273 degrees celcius)
how does the kelvin scale of the temperature define absolute zero?
0K with an increment of one Kelvin equal to an increment of one degree celcius
temperature in kelvin = temperature in degrees celcius + 273
at a constant temperature, if the volume increases…
the pressure decreases because the molecules collide less frequently with the walls over a greater area
what is Boyle’s law?
the temperature in Kelvin of a gas is proportional to the average kinetic energy of the molecules - the higher the temperature, the greater the average kinetic energy and so the faster the average speed of the molecules
