3: Particle Model of Matter Flashcards
what is density?
the mass per unit volume of a material
what is the equation for density
density = mass / volume
describe the practical to find the density of a solid
- density = mass / volume
- zero a top-ban balance and place the substance on it to measure the mass
- with regular shapes, lengths can be measured with digital callipers and multiplied to find volume
- with irregular objects: fill the Eureka can with water; place an empty measuring cylinder below its spout; now carefully lower the object into the Eureka can using a piece of string; measure the volume of displaced water in the measuring cylinder.
- once the mass and volume of the shape is known, its density can be calculated
describe the practical to find the density of a liquid
- density = mass / volume
- zero a top-ban balance and measure the mass of an empty measuring cylinder
- fill a measuring cylinder w the liquid up to a certain point e.g. 10ml - this is the volume
- now measure the mass of the measuring cylinder w the liquid inside it
- minus this value from the mass of the empty measuring cylinder - this is the mass
- now density can be calculated using the equation
what changes when a substance changes state?
only the energy of the particles
what is the internal energy of a substance?
the thermal energy store = kinetic energy (due to their random motion/vibration) + potential energy (due to the bonds between the molecules
what is the temp. of a substance related to?
the average kinetic energy of the molecules
what happens in relation to the energies of a substance when it changes state?
potential energy of the molecules increases, breaking the bonds between them; kinetic energy remains the same, meaning that the temperature will remain the same, even though the substance is still being heated
when a substance is being heated, what does the rise in temp, depend on?
the substance being heated; the mass of the substance; the thermal energy transferred to the substance
what is the definition of specific heat capacity?
the amount of thermal energy required to raise the temperature of 1kg of that substance by 1 °C
what is the equation to calculate the amount of thermal energy needed to raise the temperature of a given mass of material by a certain amount
change in energy (J) = mass (kg × specific heat capacity (J/kg °C)× change in temperature (°C)
what is meant by latent heat?
(J/kg) the energy being used to break the bonds between the molecules instead of increasing the kinetic energy of the molecules
what is specific latent heat?
(J/kg) the energy required to change the state of one kilogram of a substance
what is the specific latent heat of fusion?
(J/kg) the amount of energy required to change 1kg of the substance from solid to liquid state, without any change in the temperature
what is the specific latent heat of vaporisation?
(J/kg) the amount of energy required to change 1kg of the substance from liquid state to gas state without a temperature change
how do gases exert pressure?
they move about randomly at high speeds; as they do so, they collide with the surface of nearby walls; this exerts a force across the surface area of the walls
why when temp is increased does the pressure of a gas increase?
molecules will collide harder against any surfaces; collide with the walls more often
if you decrease the volume of a gas (whilst keeping the temperature and number of molecules fixed), what will happen to the pressure?
it will increase
what will always equal when gases are the same volume and temp?
pressure x volume
what is the equation for boyle’s law?
P1V1 = P2V2
what happens when you compress (apply force) to a gas?
work must be done on the gas to apply force to compress it; this work involves a transfer of energy which will cause the temperature of the gas to rise
what happens to the temp of a gas when expanding and why?
the gas will lose energy, which results in a temperature drop - it is doing work
what happens to the gas when you pump a bicycle pump?
it warms up - work is done on the gas
what happens when pressurised CO2 is released from a high pressure cylinder?
CO2 will freeze, forming dry ice as it does work and loses energy
