Topic 3 Flashcards
(15 cards)
What is the formula for density? (2 marks)
Density (kg/m3) = mass (kg) / volume (m3)
True or false: a materials density changing means the mass of the material changes too (2 marks)
False. The volume changes
Put the following states of matter in order of most dense to least dense and explain your reasoning: solid, liquid, gas (4 marks)
- Solid - strong forces of attraction pull the particles together into a fixed arrangment. The particles can only vibrate in their position due to a little amount of energy
- Liquid - weaker forces of attraction between the particles and higher amounts of energy in those particles mean the particles can move past each other in irregular motions, however they’re still packed together closely
- Gas - little to no forces of attraction between particles, however there is much more energy in the particles and they move around freely and travel in completely random directions
What are the steps to finding the density of a solid object? (5 marks)
- Use a balance to measure its mass
- Measure the length, width and height of the solid (if its regular). If irregular, submerge it in a eureka can filled with water. The displaced water will spill into the measuring cylinder
- (regular) Calculate the volume of the soild. (irregular) Record the volume of the water now in the measuring cylinder
- Use the density formula to find the density
What are the steps to measure the density of a liquid? (5 marks)
- Place a measuring cylinder on a balance and zero the measurements
- Pour 10ml of the liquid into the measuring cylinger and record the mass of the liquid
- Pour another 10ml of liquid into the measuring cylinder and repeat the process until the measuring cylinder is full and record the total volume and mass each time
- Use the formula for density on each of the measurements and recordings
- Finally, take an average of your calculated densities. This will give you a value for the density of the liquid
A cube has edges of length 1.5cm and average density 3500kg/m3. What is its mass to 3 decimal places? (5 marks)
1.5 x 1.5 x 1.5 = 3.375cm3
(1g/cm3 = 1000kg/m3)
3500 / 1000 = 3.5g/cm3
m = p x V
m = 3.5 x 3.375 = 11.8125
m = 11.8g
When a change in temperature occurs in a substance, what determines the change’s size? (2 marks)
The mass and the energy input
What factors can cause the state of a substance to change and what do they do to the substance? (3 marks)
Heating the substance can cause the bonds holding the particles together to be broken by the kinetic energy stores
Cooling changes the state of the substance by losing its energy and form bonds
True or false: changes of state is a chemical change (1 mark)
False. It is a physical change, meaning it doesn’t end as a new substance
Can changes in state be reversed to its original form? (1 mark)
Yes
During an experiment, a solid is heated until it melts into a liquid. Explain how heating the solid causes this change of state. (3 marks)
Thermal energy is transferred from the heat and after enough energy is transferred the kinetic energy stores break the bonds between the particles
What is the name of the energy needed to change the state of a substance? (1 mark)
Latent heat
What is the specific latent heat for changing between solid and liquid; and liquid and gas? (3 marks)
Solid–>liquid (melting or freezing: specific latent heat of fusion
Liquid–>gas (evaporating, boiling or condensing): specific lanent heat of vaorisation
What is the formula for energy needed for a substance changing? (2 marks)
Energy (E) = Mass (m) x Specific Latent Heat (L)
The specific latent heat of fusion for a particular substance is 120,000J/kg. How much energy is needed to melt 250g when it is already at its melting temperature? (2 marks)
E = m x L = 120,000 x 0.25
E = 30,000J
