1.7 Equilibria and acid-base reactions

Question 1

what is a reversible reaction?

Answer 1

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.

Question 2

what happens in dynamic equilibrium?

Answer 2

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.

Question 3

what is the proportion of products and reactants at equilibrium called?

Answer 3

The proportion of products to reactants in an
equilibrium mixture is known as the

position of equilibrium

Question 4

Le Chatelier’s Principle

Answer 4

If a system at equilibrium is subjected to a
change then the position of equilibrium will
shift to minimise that change.

Question 5

The position of equilibrium is influenced by
three factors:

Answer 5

concentration, pressure and temperature.

Question 6

what does a catalyst do?

Answer 6

catalyst decreases the time it takes to
reach equilibrium but does not alter the
position of equilibrium.

Question 7

effect of concentration change
if conc of reactant is increased?

Answer 7

If the concentration of a reactant is increased, the position of equilibrium moves to the right and more products are formed.

Question 8

what does the addition of hydrochloric acid to solution do ?

Answer 8

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.

Question 9

what does addition of sodium hydroxide do ?

Answer 9

If you add sodium hydroxide, the concentration of the H+ ions decreases, so the position of equilibrium shifts to the left

Question 10

effect of pressure change
if you increase pressure?

Answer 10

Increasing the pressure moves the position of equilibrium to whichever side of the equation has fewer gas molecules. right

Question 11

what will happen if the pressure decreases?

Answer 11

pressure will decrease if the equilibrium system contains fewer gas molecules, so
the equilibrium shifts to minimise the increase and the colour becomes lighter.

Question 12

effect of temperature increase

Answer 12

An increase in temperature moves the position of equilibrium in the endothermic
direction.

Question 13

negative enthalpy change

Answer 13

forward reaction is exothermic

Question 14

positive enthalpy change

Answer 14

reverse reaction is endothermic

Question 15

what is Kc

Answer 15

Kc is the equilibrium constant in terms of concentration.

Question 16

acid

Answer 16

proton (h+) donor

Question 17

base

Answer 17

proton (h+) acceptor

Question 18

weak acid is aq solution?

Answer 18

only partially dissociated in aq solution

Question 19

strong acid in aq solution?

Answer 19

fully dissociated (ionised) in aq solution

Question 20

what does a concentrated acid consist of?

Answer 20

large quantity of acid small quanity of water

Question 21

what does a dilute acid consist of ?

Answer 21

large quantity of water

Question 22

in a titration what must you need ?

Answer 22

one of the solutions must be a standard solution or it must have been standardised

Question 23

what is acidity?

Answer 23

The acidity of a solution is a measure of the
the concentration of aqueous hydrogen ions,
H+(aq).

Question 24

what is a standard solution?

Answer 24

A standard solution is one whose
concentration is accurately known.

Question 25

performing a titration

Answer 25

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.

Question 26

standard solution is prepared from a solid:

Answer 26

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.

Question 27

term acid

Answer 27

measure of the concentration of aq H+ ions hydrogen ions

Question 28

term dynamic equilibrium

Answer 28

the rate of the forward reaction and backward reaction is the same; there is no further change in the concentrations of reactants and products