quantative chemistry Flashcards
what is an example of a closed system
a stoppered flask
what is a closed substance
where no substances can enter or leave
what closed systems happen in an open beaker
acid-alkali neutralisation reactions
what is an example of a non-enclosed system
open flasks or boiling tubes
example of a non-enclosed system
magnesium reacts with oxygen gained from the air to from magnesium oxide
what is thermal decomposition
substance that breaks down into 2 or more substances when heated
what is uncertainty
interval within which the true value of a quantity can be expected to lie
what can be causes of uncertainty
- if a thermometer is showing the accurate temp
- exactly when a chemical reactions has finished
how to calculate uncertianty from instruments
take half the resolution and put ± e.g. resolution of 1.0cm = ±0.5cm
how to write down result with uncertainty from instruments
e.g. measured 24.0 degrees from thermometer, answer is 24.0 degreesC ± 0.5 degreesC
how to calculate uncertainty from sets of repeat measurements
use ± half the range
when is a solution formed
when a solute dissolves in a solvent
how can concentration of a solution be found
-mass of dissolved solute
./
-volume of solution
how to convert from cm^3 to dm^3
divide by 1000
how to convert from dm^3 to cm^3
multiply by 1000
what units must be used for volumes in concentration calculations
dm^3
how to calculate mass of solute
concentration in g/dm^3 * volume in dm^3
how can concentration of solution be changed
- dissolving more solute
- evaporating solvent
how to calculate number of particles
amount of substance in moles * avogadro constant * subscript number
when to use Ar instead of Mr
for metals or separate atoms
how to calculate masses of substance in a balanced equation
relative formula mass * amount
what is a limiting reactant
a reactant that has been used up
what is excess
reactant that is left after a reaction
what does the mass of a product depend on
the mass of the limiting reactant
how to calculate balancing numbers
1- write the formula of substances
2-calculate the amount in moles
3-divide both by the smaller amount
how to convert from mol/dm^3 to g/dm^3
multiply by relative formula mass
how to convert from g/dm^3 to mol/dm^3
divide by relative formula mass
how to calculate atom economy
(total Mr of desired product / total Mr of all reactants) * 100
what is the theoretical yield
maximum possible mass of a product that can be made in a reaction
reasons why mass of product is less than theoretic yield
- reaction not completing as it is reversible
- product may be lost when separated from reaction mixture
- some reactants may react in different ways different to expected
what factors depend what chosen pathway you take
- percentage yield
- atom economy
- rate of reaction
- equilibrium position
- usefulness of by-products
what is avagadro’s law
in a given temperature and pressure equal volumes of different gases contain equal numbers of molecules
what is the molar volume
volume occupied by one mole of any gas at room temp and pressure (24dm^3)
how to calculate volume of gas
amount in mol * molar volume
how to calculate amount of gas
volume / molar volume
