1.7 Equilibria and acid-base reactions Flashcards
what is a reversible reaction?
can be made to go in either direction depending on the conditions. When you have a reversible reaction in a closed system, a dynamic equilibrium is established.
what happens in dynamic equilibrium?
The rate of the the forward reaction and backward reaction is
the same; there is no further change in the
concentrations of reactants and products.
what is the proportion of products and reactants at equilibrium called?
The proportion of products to reactants in an
equilibrium mixture is known as the
position of equilibrium
Le Chatelier’s Principle
If a system at equilibrium is subjected to a
change then the position of equilibrium will
shift to minimise that change.
The position of equilibrium is influenced by
three factors:
concentration, pressure and temperature.
what does a catalyst do?
catalyst decreases the time it takes to
reach equilibrium but does not alter the
position of equilibrium.
effect of concentration change
if conc of reactant is increased?
If the concentration of a reactant is increased, the position of equilibrium moves to the right and more products are formed.
what does the addition of hydrochloric acid to solution do ?
the position of equilibrium moves to the right. More H+ ions have been added so the equilibrium shifts to decrease the concentration of the H+ ions and the solution turns more orange.
what does addition of sodium hydroxide do ?
If you add sodium hydroxide, the concentration of the H+ ions decreases, so the position of equilibrium shifts to the left
effect of pressure change
if you increase pressure?
Increasing the pressure moves the position of equilibrium to whichever side of the equation has fewer gas molecules. right
what will happen if the pressure decreases?
pressure will decrease if the equilibrium system contains fewer gas molecules, so
the equilibrium shifts to minimise the increase and the colour becomes lighter.
effect of temperature increase
An increase in temperature moves the position of equilibrium in the endothermic
direction.
negative enthalpy change
forward reaction is exothermic
positive enthalpy change
reverse reaction is endothermic
what is Kc
Kc is the equilibrium constant in terms of concentration.
acid
proton (h+) donor
base
proton (h+) acceptor
weak acid is aq solution?
only partially dissociated in aq solution
strong acid in aq solution?
fully dissociated (ionised) in aq solution
what does a concentrated acid consist of?
large quantity of acid small quanity of water
what does a dilute acid consist of ?
large quantity of water
in a titration what must you need ?
one of the solutions must be a standard solution or it must have been standardised
what is acidity?
The acidity of a solution is a measure of the
the concentration of aqueous hydrogen ions,
H+(aq).
what is a standard solution?
A standard solution is one whose
concentration is accurately known.
performing a titration
Pour one solution, say, an acid, into a burette, using a funnel, making sure that the jet is filled.
Remove the funnel and read the initial burette volume.
Use a pipette to add a measured volume of the other solution, say, a base, into a conical flask.
Add a few drops of indicator to the solution in the flask.
Run the acid from the burette into the solution in the conical flask, swirling the flask.
Stop when the indicator just changes colour (the endpoint of the titration).
Read the final burette volume and calculate the volume of acid added (known as the titre).
Repeat the titration, making sure that the acid is added dropwise near the endpoint, until you have at least two readings that are within 0.20 cm3 of each other.
Calculate a mean titre.
standard solution is prepared from a solid:
Calculate the mass of the solid required
and accurately weigh this amount into a
weighing bottle.
Transfer the solid into a beaker and wash
out the weighing bottle so that all of the
weighed solid is transferred.
Add water and stir until all the solid dissolves.
Pour all the solution carefully into a volumetric (graduated) flask, washing all
the solution out of the beaker and off the stirring rod.
Add water until just below the graduation mark.
Add water drop by drop until the graduation mark is reached.
Invert the flask several times to mix the solution thoroughly.
term acid
measure of the concentration of aq H+ ions hydrogen ions
term dynamic equilibrium
the rate of the forward reaction and backward reaction is the same; there is no further change in the concentrations of reactants and products
