Topic 1 Flashcards
Formula for pressure? Give units for each of the 5 values
PV = nRT
Pressure - pascals n = moles R = 8.31 Joules per kelvin mole (J k^-1 mol^-1) V = m^3 T = kelvin
Describe relationship between pressure, temperature and volume
Volume is INVERSELY proportional to pressure
temperature is directly proportional to volume
temp is DP to pressure
V is directly proportional to 1/P and vice versa
Trick for limiting reactant?
If asked to find limiting reactant, calculate actual number of moles of each reactant, then divide by coefficient to find the limiting reactant based on which one is smaller. but REMEMBER: when asked to find the yield of one of the products you use the ACTUAL number of moles and do the ratio thing with that, not with the divided coefficient values.
How do you convert from cm3 to m3 for the pressure equation?
cm3 -> m3: divide number by 10^6
What is the standard temperature and pressure? (STP)
Temp - 273 kelvin
Pressure - 1 x 10^5 pascals
Equation for molar volume of a gas?
Molar volume = moles x 22.7
What does the 22.7dm3 represent?
At STP, 1 mole of any gas occupies 22.7 dm^3 volume
How to determine molar mass of a gas experimentally?
To collect the gas, a measuring cylinder is inverted and filled with water
measuring cylinder filled with known volume of gas from a cigarette lighter
mass of lighter recorded before and after
find change in mass in lighter
Find volume collected - convert to m3
convert temp to kelvin
R = 8.31 J k-1 mol-1
P = atmospheric pressure of water - vapour pressure
substitute these into M = mRT/PV
find molar mass VOILAAAA
How to calculate percentage area of the molar mass method?
Experimental - theoretical/theoretical x 100
Why is the experimental value less than the theoretical value for molar mass?
Lighter not dried completely before weighing
Liquid may be a mixture of propane and butane
Pressure of gas not equalised with pressure of room
Assumptions of the ideal gas law? (PV=nRT)
Particles are in constant, straight line, random motion
Collisions between particles are elastic with no loss in kinetic energy
No intermolecular forces acting between particles
Under what two conditions do ideal gases deviate the most?
High pressure
low temperature
Under these conditions, product of PV/RT is no longer equal to 1
Describe the ideal gas deviation curve
A low temperature and a high pressure cause the most deviation
Ideal gases have virtually no what?
volume
intermolecular forces
however, at high pressures, space between particles is reduced and volume of real gases cannot be negligible
real gases deviate most from ideal gas behaviour under HIGH PRESSURE and LOW TEMP
- intermolecular forces have an effect on the pressure of a real gas compared to an ideal gas
- IMF reduces collisions with walls of container
- pressure exerted decreases so observed pressure is less for a real gas than ideal gas
Definition of an element
A substance that cannot be broken down by chemical means into simpler substances
Definition of a compound
2 or more elements chemically bonded together
Definition of a mixture
A mixture contains more than one element and/or compound not chemically bonded together and so retain their individual properties. Their composition is not fixed
Homogenous mixtures + example?
Have uniform properties and composition e.g: air, brine, amalgum.
Heterogenous mixtures + example?
Have non-uniform composition and properties. e.g: salt and sand, oil and water. Properties not the same throughout. Can be separated
Describe the difference in property of components of these mixtures and the technique used to separate them:
i) Sand and salt
ii) Hydrocarbons in crude oil
iii) iron and sulfur
iv) pigments in food colouring
v) Different amino acids
i) Solubility in water, solution and filtration
ii) Boiling point, fractional distillation
iii) magnetism, response to a magnet
iv) absorption to solid phase, chromatog
v) net charge at fixed pH, gel electrophoresis
Describe the composition of a solid
Particles closely packed together
Inter-particle forces strong
Particles vibrate in position
They have a fixed shape, cannot flow
Fixed volume
Describe the composition of a liquid
Particles more spaced
Weaker inter-particle forces
Particles can slide over each other
No fixed shape
Fixed volume
Describe the composition of a gas
Particles spread out
Inter-particle forces are negligible
Particles move freely
No fixed shape
No fixed volume
Describe the kinetic theory of matter
It describes that the average kinetic energy of the particles is directly proportional to the temperature of the system. The state of matter at a given temperature and pressure is determined by the strength of forces that may exist between the particles, known as inter-particle forces.
Fluids are solids, liquids or gases?
Liquids and gases - basically any substance that can flow and take the shape of their container.
What is sublimation?
Solid to gas
What is condensation
Gas to a liquid
Liquid to a gas?
Evaporation
Gas to solid?
Deposition
Liquid to solid?
Freezing
Gas to a liquid
Condensation
Difference between evaporation and boiling?
Evaporation involves the change of a liquid to a gas but unlike boiling, evaporation occurs only at the surface and takes place at temperatures below the surface. Boiling on the other hand is when particles leave throughout the body of the liquid which is why the bubbles occur. Boiling occurs at a specific temperature, determined by when the vapour pressure reaches the external pressure.
Describe the energy input and temperature graph
i) As the solid is heated, the vibrational energy of its particles increases and so the temperature increases
ii) This is the melting point. Vibrations are sufficiently energetic for the molecules to move away from their fixed positions and form a liquid. Energy added during this stage is used to break the inter-particle forces and NOT to raise the kinetic energy. Temperature stays constant
iii) As the liquid is heated, the particles gain kinetic energy and so the temperature increases
iv) This is the boiling point. Now there is sufficient energy to break all of the inter-particle forces and form a gas.
v) As the gas is heated under pressure, the kinetic energy of its particles continues to rise and so does temperature
PRESSURE REMAINS CONSTANT
Describe the problems with the butane molar mass experiment
Butane can dissolve in the water, causing the Mr value to raise. Use colder water in which it is less soluble
Some air/water vapour can be collected with the gas, decreasing the Mr, use chilled boiled water to ensure less air is present
Butane gas escapes as the cylinder was tilted, causing molar mass to be greater because the decrease in mass of the lighter would be exaggerated.
What could cause the Molar Mass of butane to be lower than expected
If pressure and volume are high.
Describe the relationship between density and temperature
inversely proportional
Does doubling temperature from 25 degrees to 50 degrees celcius change volume of a gas?
No, because when temperature is converted to kelvin, it is actually not doubled so volume does not double
