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Define Compound
a pure substance formed when two or more elements combine chemically
How do you ratios relate to elements combining to form compounds?
each element combines with each other in a fixed ratio
Define Mixture
two or more substances mixed together but not chemically bonded so retain their individual properties
Define Homogeneous Mixture
a mixture that has the same uniform composition throughout and consists of one phase, such as a solution or mixture of gases
How can homogeneous mixtures be separated?
through physical means, e.g. distillation, crystallisation and fractional distillation
Define Heterogeneous Mixture
a mixture that does not have uniform composition and consists of separate phases e.g. sand in water
How can heterogeneous mixtures be separated?
by mechanical means e.g. filtration or using a magnet
What is cooling?
a substances’ energy is removed and particles lose energy - temperature decreases
What is freezing?
liquid turns to a solid, particles lose energy, temp decreases
What is melting?
solid turns to a liquid, particles gain energy, temp increases
What is sublimation?
when a solid turns to a gas, particles gain energy, temp is increased
What is deposition?
when a gas turns to a solid, particles lose energy, temp is decreased
What is boiling/evaporating?
when a liquid turns into a gas, particles gain energy, temp increases
What is condensing?
when a gas turns into a liquid, particles lose energy, temp is decreased
What temp does melting occur? (water)
above 0 degrees celsuis
What temp does boiling occur? (water)
around 100 degrees celsius
What temp does freezing occur? (water)
sub 0 degrees
Balance SF4 + H20 → SO2 +HF
SF4 + 2H20→ SO2 + 4HF
Define Relative Atomic Mass
the average mass of the naturally occurring isotopes of an element relative to the mass of 1/12 of an atom or carbon 12
Define Mole
the amount of substance that contains 6.02 x 10 ^23 particles
Define Avogadro’s Constant
a unit with the value 6.02 x 10^23
give the equation to find number of moles
no. of moles = mass of substance/molar mass
give the equation to find the mass of 1 molecule of a substance
mass of 1 molecule = Mr/6.02 x 10^23
What is empirical formula?
the simplest whole number ratio of the elements present in a compound
What is molecular formula?
the total number of atoms of each element present in a molecule of the compound
How do you find moles when volume of gases are given?
no.of moles = volume of gas (dm^3) / 22.7 (dm^3)
How do you find moles when concs and vols of solutions are given?
no. of moles = conc x volume
Define theoretical yield
the maximum possible amount of product formed
Define experimental yield
the actual amount of product formed in the reaction
How do you calculate the percentage yield?
experimental yield/theoretical yield x100
Define limiting reactant:
the reactant that is not in excess and therefore determines the yield of product
How do you find the limiting reactant?
divide the no. of moles of each reactant by its coefficient in the chemical equation and the smallest number equals the limiting reactant
What does a 0.100M solution mean?
The concentration = 0.100mol/dm3
Why do people use ‘ideal gases’?
they are used to model the behaviour of real gases and be used in calculations
What two assumptions are made about ideal gases?
the molecules themselves have no volume and no forces exist between them - apart from when they collide
In what conditions do gases deviate most from ideal behaviour?
at high pressure and low temps - this is when a gas is most like a liquid so the particles are close together and forces between molecules and volume of molecules will be most significant
Give Avogadro’s Law (gas)
equal volumes of ideal gases measured at the same temperature and pressure contain the same number of particles (no.of moles of an ideal gas is proportional to its volume)
What is the relationship between pressure and volume?
inversely proportional - if pressure doubles, volume halves
What is the relationship between volume and temperature?
directly proportional - if temperature is doubled volume will double
What is the relationship between temperature and pressure?
directly proportional - if temperature is doubled, pressure will double.
Give the overall gas law equation
P1 x V1 / T1 = P2 x V2 / T2
Give the ideal gas equation
PV = nRT
What is the value of R (gas constant)
8.31 JK^-1mol^-1
What unit does volume have in the ideal gas equation?
m^3
What unit does pressure have in the ideal gas equation?
Pa
What unit does temperature have in the ideal gas equation?
K
Define Standard Solution
a solution of known concentration
How do you work out concentrations in mol dm^-3?
conc = moles/volume
How do you work out concentrations in g dm^-3
conc - mass (g)/volume
how do you find concentration in ppm? (gas)
conc ppm = vol of gas / vol of air x 10^6
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