Equilibria and Acid Base Reactions

What is a reversible reaction:

A reversible reaction is one which can be made to go in either direction depending on the conditions.

Dynamic Equilibrium

when the rate of the forward reactions and the rate of the backwards reaction is the same

Position of Equilibrium

the proportion of products to reactants in an equilibrium mixture

What is 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.

What factors influence the position of equilibrium?

Concentration

Pressure

Temperature

What effect does a catalyst have on equilibrium?

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

How does concentration change affect position of equilibria?

As concentration of a reactant increases, the position of equilibrium moves to the right and more products are formed

What would happen if you add HCl to

2CrO₄²⁻(aq) + 2H+(aq) ⇌ Cr₂O₇²⁻(aq) + H2O(l)

yellow orange

The position of equilibrium moves to the right as more H+ ions have been added so equilibrium shifts to decrease the concentration of the H+ ions.

What would happen if you add NaOH to the reaction

2CrO₄²⁻(aq) + 2H+(aq) ⇌ Cr₂O₇²⁻(aq) + H2O(l)

The concentration of the H+ ions decreases so the position of equilibrium shifts to the left

What is the effect of pressure on position of equilibrium?

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

What would increasing pressure have on this reaction:

2NO₂(g)⇌ N₂O₄

If the pressure is increased, position of equilibrium moves to the right

When does pressure decreases in terms of position of equilibrium?

Pressure decreases if the equilibrium system contains fewer gas molecules so the position of equilibrium will shift from the right to left to minimise change

What is the effect of temperature on the position of equilibrium?

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

How would temperature increase affect this reaction:

N₂(g) + 3H₂(g) ⇌ 2NH₃(g) ΔH = –92 kJ mol⁻¹

Ans: As the enthalpy change is negative, the forward reaction is __________. If the temperature increases, the position of equilibrium moves to the ______. The system opposes the change by absorbing ______ _____, favouring the backward reaction and decreasing the ____-.

exothermic

left

extra heat

yield

An increase in temp will always favour the _______________ as temperature will decrease as heat is ________. Equilibrium shifts to the ____.

endothermic

absorbed

left

A decrease in temperature will favour the __________ reaction as this will increase the temperature in the __________ . Equilibrium shifts to the ______

exothermic

system

right

What is Kc

Equilibrium constant

What is Kc affected by

Temperature

What is the formula of Kc

Products

Reactants

What is the pH scale?

measure of how many H+ ions

What is the formula for pH

-log10 [H+(aq)]

What is the formula of H+ ions

10^-pH

What is the acid dissociation constant?

Equilibrium of acids in an aqueous solutions

Reactants

Products

What is the difference between strong acid and weak acid?

Strong acids completely dissociate in water, whereas weak acids partially dissociate

What is an acid?

Proton donor

What is a base

proton acceptor

What is the difference between a concentrated acid?

consists of a large quantity of acid and small quantity of water

What is a standard solution?

A standard solution is one whose concentration is accurately known.

Steps of making a standard solution:

First, you need to __________ the mass of the solid you need.

• Then, carefully __________ that amount into a weighing bottle.

• Next, __________ the solid into a beaker.

• Wash out the weighing bottle to make sure __________ of the solid gets transferred.

• Add __________ to the beaker and stir until the solid __________.

• Pour the solution into a __________ flask.

• Wash out the beaker and stirring rod to get all the __________.

• Add water until it's just below the __________ mark on the flask.

• Then, add water __________ by __________ until you reach the graduation mark.

  • Finally, __________ the flask to mix the solution well.

calculate, weigh, transfer, all, solid, dissolved, volumetric, solid, graduation, drop, drop, invert

Steps to follow a titration:

Pour one solution, say, an ____, into a ________, using a ______, making sure that the jet is filled. Remove the funnel and read the ______ burette volume.

Use a _______ to add a measured volume of the other solution, say, a _____, into a ______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, ________ the flask.

Stop when the indicator just changes ________ (the endpoint of the titration).

acid, biurette, funnel, intial, pipette, base, conical, indicator, swirling, colour