What can be changed in a reaction to alter the equilibrium position?
Concentration, temperature, pressure/volume (only applies to gases)
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What happens to the equilibrium position when the product concentration is increased?
The reverse reaction increases and equilibrium moves to the left
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What does Le Chatelier's principle state?
If an equilibrium system is subjected to a change, the system will adjust itself to partially oppose the effect of the change
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What happens to the equilibrium position when the reactant concentration is increased?
The forward reaction increases and equilibrium moves to the right
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On an equilibrium graph how do you know the reaction has reached equilibrium?
When equilibrium is established the concentration lines are horizontal
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What is meant by an "open system"?
An open system allows matter and energy to be exchanged with the surroundings
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Are all reactions reversible?
No, for example due to the formation of energetically stable products or loss of products into the environment
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What is a "closed system"?
A reaction vessel that does not allow the reactant or product particles to escape
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Give an example of an "open" system.
A flask with no lid that allows heat and gas products escape
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What type of system is it when energy can escape but not matter?
Closed system
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What is meant by the term "reversible reaction"?
Reactions in which the conversion of reactants to products and products to reactants occur simultaneously.
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Are physical changes reversible?
Generally they are reversible as chemical bonds remain unchanged
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Why is a substance in a system more likely to react when the temperature is higher?
The particles of that substance have more kinetic energy, causing them to collide more often with the other particles in the system, making the reaction occur
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How are equilibrium reactions symbolised?
Equilibrium reactions are symbolised by ⇌
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What is activation energy?
The minimum amount of energy required in the collision between reactants for a reaction to occur
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What can you measure using observation in equilibrium reactions?
You can observe whether the forward or reverse reaction has occurred if the reactants and products have different colours
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In a reaction where a gas is produced what type of system is required for equilibrium to be reached?
A closed system
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What does Kc represent?
The equilibrium constant
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When is a state of dynamic equilibrium reached?
A state of equilibrium is reached when the rate of the forward and reverse reactions are equal
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How can you measure the concentration of an equilibrium using pH?
You can measure the change in pH and calculate the H3O+ concentration, then use simple stoichiometry
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Can forward and reverse reactions occur at the same time?
Yes, a forward and reverse reaction can occur at the same time if the reaction occurs within a closed system
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What is the impact on the equilibrium position when a catalyst is added to a reaction in a closed system?
There is no impact on the equilibrium position. Equilibrium will only be reached faster
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What concentrations are not included when calculating the equilibrium constant?
Concentrations of pure liquids and solids are not included, water is only included if it is a product such as in condensation reactions
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Where can the elements with the lowest ionisation energy be found on the periodic table?
"Bottom left e.g. Cs, Rb, Ba"
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What kind of ionisation energy makes elements lose electrons more readily?
Low ionisation energy
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Is the equilibrium constant value largest when the concentration of reactants is larger than the products?
No
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What energy is required to remove an electron from an element?
First ionisation energy
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"True or False? The stronger the electronegativity, the more readily the element will accept electrons."
TRUE
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If Kc is larger than 104 is there significantly more reactant or product?
Product
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"True or false? Is the Kc of a reaction temperature dependent?"
TRUE
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What does RICE stand for?
Reaction, initial concentration, change in concentration, equilibrium concentration
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What happens to the equilibrium position for an endothermic reaction when heat is added?
The equilibrium position will move towards the product side as heat is stored in the molecule
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What can you do to increase the concentration of gas in a closed system?
Decrease the volume
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What happens when the pH of a solution is equal to the pKa of an indicator?
The indicator will change colour
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What type of substance does this equation represent? BOH → B+(aq) + OH-(aq)
A strong base
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What is the definition of a weak base in terms of its Kb?
Low Kb - Weak bases
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What is the relationship between the pH range of an acid-base indicator and its pKa value?
A higher pKa correlates to a higher end point of the indicator
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What is the definition of a weak acid in terms of its Ka ?
Ka < 1 Weak acids
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What is a conjugate acid?
An acid formed when a base accepts a proton (H+) B: + H2O → B:H+ + OH- (B:H+ is the conjugate acid)
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What is an amphiprotic substance?
A substance that can act as either an acid or a base
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What is an example of a common amphiprotic substance?
Examples could include - water, amino acids and hydrogen carbonate ions (HCO3- )
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What is a conjugate pair?
Two species that differ by a proton (H+)
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Identify the conjugate acid produced in this reaction: NH4+ + OH- ⇌ NH3 + H2O
H2O
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What is a conjugate base?
A base formed by removing a proton (H+) from an acid
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Identify the conjugate base produced in this reaction: NH4+ + OH- ⇌ NH3 + H2O
NH3
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How does the Brønsted-Lowry model define an acid and a base?
Acids as any species that can donate protons (H+). Bases as any species that accept protons (H+)
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What is the conjugate base of CH3COOH?
CH3COO-
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What is the conjugate acid of the following base: OH- ?
H2O
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Why is water a weak electrolyte?
It can self-ionise, but equilibrium lies to the left H2O ⇌ H+(aq) + OH-(aq)
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What is Kw?
Kw is the ionic product constant of water. It is the equilibrium constant for the self-ionisation of water. Kw can be used to calculate the concentration of hydrogen ions from the concentration of hydroxide ions in a solution
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How is pH calculated?
The pH of a solution can be calculated from the concentration of hydrogen ions using the relationship pH = -log10 [H+ ]
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How is pOH calculated?
pH = -log10 [OH-]
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Under what circumstances could the numerical value of Kw differ?
Different temperatures. Kw is 10-14 at just below 25oC
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What is self-ionisation of water?
Self-ionisation of water refers to the reaction in which a water molecule loses a hydrogen ion (leaving OH-) and the hydrogen ion immediately reacts with another water molecule to form a hydronium ion (H3O+ )
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What is pH?
pH is a figure expressing the acidity or alkalinity of a solution on a logarithmic scale
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How is [H+ ] calculated?
[H+ ]= 10^(-pH)
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How is [OH- ] calculated?
[OH-] can be obtained using the pH or pOH value: pH + pOH = 14 pOH = 14 - pH pOH= --log10 [OH- ] [OH-] = 10^(-pOH)
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pH + pOH = ?
14 or Kw (at just below 25oC)
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How do we calculate Kw?
Kw = Ka x Kb
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How do we calculate concentration?
C = n / V
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What are acid-base indicators?
Weak acids or bases, which dissociate slightly in water and form ions
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How are strong acids defined?
Strong acids are defined fully ionising / dissociating (Ka > 1 )
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How are weak bases defined?
Weak bases are defined as having a low Kb
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How do you calculate Ka?
Ka = [H3O+ ] x [A-] / [HA]
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How do you calculate Kb?
Kb = [BH+ ] x [OH-] / [B]
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How are weak acids defined?
Weak acids are defined as having a Ka < 1
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How are strong bases defined?
Strong bases are defined as having a high Kb
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What type of substance does this indicator represent? HIn ⇌ H+(aq) + In-(aq)
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