3: Particle Model of Matter

Question 1

what is density?

Answer 1

the mass per unit volume of a material

Question 2

what is the equation for density

Answer 2

density = mass / volume

Question 3

describe the practical to find the density of a solid

Answer 3

• 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

Question 4

describe the practical to find the density of a liquid

Answer 4

• 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

Question 5

what changes when a substance changes state?

Answer 5

only the energy of the particles

Question 6

what is the internal energy of a substance?

Answer 6

the thermal energy store = kinetic energy (due to their random motion/vibration) + potential energy (due to the bonds between the molecules

Question 7

what is the temp. of a substance related to?

Answer 7

the average kinetic energy of the molecules

Question 8

what happens in relation to the energies of a substance when it changes state?

Answer 8

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

Question 9

when a substance is being heated, what does the rise in temp, depend on?

Answer 9

the substance being heated; the mass of the substance; the thermal energy transferred to the substance

Question 10

what is the definition of specific heat capacity?

Answer 10

the amount of thermal energy required to raise the temperature of 1kg of that substance by 1 °C

Question 11

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

Answer 11

change in energy (J) = mass (kg × specific heat capacity (J/kg °C)× change in temperature (°C)

Question 12

what is meant by latent heat?

Answer 12

(J/kg) the energy being used to break the bonds between the molecules instead of increasing the kinetic energy of the molecules

Question 13

what is specific latent heat?

Answer 13

(J/kg) the energy required to change the state of one kilogram of a substance

Question 14

what is the specific latent heat of fusion?

Answer 14

(J/kg) the amount of energy required to change 1kg of the substance from solid to liquid state, without any change in the temperature

Question 15

what is the specific latent heat of vaporisation?

Answer 15

(J/kg) the amount of energy required to change 1kg of the substance from liquid state to gas state without a temperature change

Question 16

how do gases exert pressure?

Answer 16

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

Question 17

why when temp is increased does the pressure of a gas increase?

Answer 17

molecules will collide harder against any surfaces; collide with the walls more often

Question 18

if you decrease the volume of a gas (whilst keeping the temperature and number of molecules fixed), what will happen to the pressure?

Answer 18

it will increase

Question 19

what will always equal when gases are the same volume and temp?

Answer 19

pressure x volume

Question 20

what is the equation for boyle’s law?

Answer 20

P1V1 = P2V2

Question 21

what happens when you compress (apply force) to a gas?

Answer 21

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

Question 22

what happens to the temp of a gas when expanding and why?

Answer 22

the gas will lose energy, which results in a temperature drop - it is doing work

Question 23

what happens to the gas when you pump a bicycle pump?

Answer 23

it warms up - work is done on the gas

Question 24

what happens when pressurised CO2 is released from a high pressure cylinder?

Answer 24

CO2 will freeze, forming dry ice as it does work and loses energy