Quantitive chemistry and chemical changes Flashcards
only basics use free science lessons to go over in full detail
how do you calculate the percentage mass of an element in a compound
atomic mass x number of atoms of the element / relative formula mass of the compound
how do you calculate the number of moles
mass in g / relative formula mass
in an exothermic reaction is heat given in or out
given out
in an endothermic reaction is heat given in or out
taken in
does an exothermic reaction transfer energy to or away from the surroundings
transfers energy to the surroundings usually by heating
does an endothermic reaction take energy form the surroundings or transfer energy to the surroundings
the reaction takes energy from the surrounding
this is shown by a fall in temperature
give an example of an exothermic reaction
hand warmers
self heating cans
give an example of an endothermic reaction
sports injury packs
explain a exothermic reaction
this reaction is exothermic because energy needed to break the bonds is less than energy released in bond formation
explain a endothermic reaction
energy released in bond formation
is less than
energy needed to break the bonds
are endothermic reaction energy changes positive or negative
positive +
are exothermic reaction energy changes positive or negative
negative -
explain bond energies
when we want to break a chemical bond, it requires energy normally endothermic
this then releases energy normally exothermic
every chemical bond has an energy value
this tells us the energy needed to break the bond
is breaking bonds endo or exo themic
endothermic +
why is it not always possible for a 100% yield
product is lost in transfer
give the equation of percentage yield
product that was actually produced / product that should of been produced x 100
why can we not achieve more than 100% yield
because it means you would have created atoms and that is not possible
state what is meant by an exothermic reaction
an reaction that releases energy
in energy transfer diagrams, exothermic,
do the products have more or less energy than the reactants
less
because energy is being transferred from the reaction to the surroundings
in energy transfer diagrams, endothermic
do the products have more or less energy than the reactants
more
because energy has been taken in from the surroundings
if the products have more energy than the reactants what does this mean
energy has been taken in from the surroundings
energy increases
endothermic
positive
if the products have less energy than the reactants what does this mean
energy is being transferred from the reaction to the surroundings,
energy decreases
- exothermic
negative
if a reversible reaction is exothermic in one direction what happens to the other direction
it is endothermic in the opposite direction
the same amount of energy is transferred in each case
what is a dynamic equilibrum
rate of forward reaction is equal to rate of backward reaction in a closed system
what happens if temperature is increased in an reversible reaction
if temperature increases, endothermic reaction is favoured
what happens if temperature is increased in an exothermic reaction
if temperature increases, exothermic reaction is favoured
what is the effect of pressure
pressure favours the reaction which produces fewer molecules
meaning the reaction will produce more of the favoured reactions
what happens in a dynamic equilibrium
concentration of reactants and products stay constant
what must happen in a dynamic equilibrium
reaction must be reversible
reaction must undergo in a closed system so no change of matter, but energy can still be exchanged
what is the calculation of concentration.
mass (g) / volume (dm3)
if we increase the mass of solute and keep the volume the same what happens to the concentration
it stays the same
if we increase the volume of solution and keep the mass of solute the same what will happen to the concentration
it will decrease
what is atom economy
is the measure of the amount of starting materials that end up as useful products
what is the equation of atom economy
mr of desired products / mr of all reactants (from equation) x 100
what is the equations for atomic mass
(Ar x Adundance) + (Ar x abundance) // 100
what is the equation for moles in solids
mass / Mr
what is the equation for moles in gases
if in dm3
volume dm3 / 24dm3
if in cm3
volume cm3 / 24000
what is the equation for concentration?
mols or mass / volume dm3
what is a reversible reaction
when the products can react together to make the reactants
what is a closed system
when no exchange of matter can occur only energy can be transferred
effect of increasing temperature in a dynamic equilibrium
a increase of temperature favours endothermic reaction
effect of increasing pressure in a dynamic equilibrium
an increase in pressure favours the side with the least moles (molecules)
effect of concentration in a dynamic equilibrium
an increase in concentration of reactants
move the equilibrium forwards direction
to make more products
explain in terms of bond making and breaking why a reaction is endothermic
energy released in bond formation
is less than
energy needed to break the bonds
explain in terms of bond making and breaking why a reaction is exothermic
energy released in bond formation
is more than
energy needed to break the bonds
explain why a non metal has a low boiling point
simple molecular structure
weak intermolecular forces
little energy needed to overcome these
