P1.2 Flashcards
Formula for density and SI units
Density= Mass/Volume
Kg/ m3
Symbol in Greek is rho (P)
Why are substances denser as solids than as liquids or gas
Because when states change the mass don’t, so it will be the same mass but in more volume, meaning less density
This is true except for ice, which is actually less dense then water- due to the way hydrogen bonds work.
PRACTICAL: How to measure density of an object
Mass: mass balance
Volume: 1) for liquid, use a measuring cylinder, 2) use math formulas 3) for a random object, use eureka can:
An object submerged in water will displace a volume of water = to its own volume. Fill up a eureka can a bit over, lit it drop. Then with a piece of string slowly lower object and collect water in a beaker. Do three times for mean.
Finally use formula.
Difference between energy and temperature?
What happens when you heat a substance up.
The energy in a substance’s thermal store is measured in joules , depends on the particles kinetic energy stores.
Temperature is a measure of the average kinetic energy of particles.
- when you heat a substance up, energy is transferred to the kinetic stores of the particles, moving them more, increasing the temperature. The overall thermal store for the substance increases too. Eventually, particles have enough kinetic energy to overcome their intermolecular forces of attraction and change state.
Formula for specific heat capacity and SI Units
Water?
E= MC change of T (mcat)
Change in thermal energy store (J)= Mass( Kg) X specific heat capacity ( J/KgC(k)) X temp (C)
It is the change of thermal energy needed tk raise 1 kg of a substance by 1 c°
Water= 4200 J/kgc
What does specific heat capacity tell you?
How resistant a material is to a change of temperature. This is why saucepans have very low capacity it’s so they warm quickly
PRACTICAL: How to find out specific heat capacity of a substance (important )
What makes the practical better? (3)
1) MASS= use a mass balance to measure mass of substance
2) Use an electric heater with a joulemeter, attach this to the insulating container with the liquid in.
3) put a thermometer there and use it to measure initial temp of the substance.
4) Turn on the Power for heater. Let the Temperature rise for say 10 degrees, then turn the heater off and record the energy used.
5) now calculate the specific heat capacity using
formula. REPEAT 3 TIMES FOR A MEAN MAKE IT better test.
You need to reduce heat loss to surroundings, therefore use an insulating cup like a polystyrene cup packed with COTTON WOOL. You can also use conducting gel between like a solid and the heater, and finally use a lid to further reduce energy loss which is systematic error.
Specific latent heat
Thermal energy for a change if state (J)= mass (kg) X specific latent heat (J/KG)
Shows the amount of energy needed to change 1 kg of a substance by a state, either vaporisation (liquid to gas) or fusion (solid to liquid)
Why does temp not change between change of states even though toy are increasing energy?
Energy is being transferred to particles kinetic energy stores, which makes them move around faster. However, the merge is no longer increasing the temperature as it is being used to break the intermolecular bonds between molecules. The temperature won’t rise until all of the molecules have broken their bones, causing flat lines on the graph. Similarly when condensing, energy is being released to make bonds, so until all of the bonds have formed again, temp won’t decrease…
