CHEMISTRY

UNIT 3&4

UNIT 3

TERM 4

Discriminate between open or closed chemical systems.

Open:

• The chemicals can be either added or lost, allowing heat to enter or leave

• exchanges both energy and matter

Closed:

• System where all involved chemicals are contained in a fixed space, resulting in no add or loss of chemicals

• only energy is exchanged

 Identify wether physical changes and chemical changes are reversible or irreversible. provide an example

• Physical - usually reversible due to products being able to converted back into reactants, for example ice.

• Chemicals - while some are reversible many are irreversible due to forming new substances with different amounts of energy, molecule structure, and bonding.

Symbolise equilibrium equations using forward, reverse and reversible symbols in balanced chemical equations using H₂O (l) = H⁺(aq) + OH^- (aq).

Reversible reaction - H₂O (l) ⇌ H⁺(aq) + OH^- (aq)

Forward reaction - H₂O (l) → H⁺(aq) + OH^- (aq)

Reverse reaction - H⁺(aq) + OH^- (aq) → H₂O (l)

 Explain observable properties and the characteristics of physical and chemical systems in a state of equilibrium.

the Observable properties of:

• colour intensity, temperature, pressure, and and state of matter (due to phase changes) remain constant due to the characteristics being equal as the concentration of reactants and products remain constant

indicate that the characteristic of:

• forward rate = reverse rate (process still occurring except at same speed)

these suggest that the system is in a state of equilibrium

what happens to the physical change of a reversible chemical reaction when it reaches a state of dynamic equilibrium in a closed system? refer to the relative concentrations of products and reactants.

• The observable features remain constant due to the balance between forward and reverse reaction (equal to each other)

• As the concentration of reactants and products remain at a fixed value

Distinguish between equilibrium and dynamic equilibrium - When must it be displayed

• equilibrium - general state of balance and numbers/amount stop changing

• dynamic - occurs in closed system where forward reaction = reverse reaction, specific type of balance and movement still occurs.

• rate of reaction vs time and rate of reaction vs concentration

Explain the reversibility of chemical reactions by considering the activation energies of the forward and reverse reactions.

• chemical reaction is reversible (both forward and reverse reactions) if the particles are able to overcome the Ea at a specific temperature due to the Ea being low.

• Due to the low Ea values which allow the particles to contain sufficient energy, a successful collision can occur allowing the establishment of dynamic equilibrium

 Key points when analysing data and interpreting graphical representations of relative changes in the concentration of reactants and product against time, to determine the position of equilibrium.

• When equilibrium is reached

• Determine the position of equilibrium

-favours the reactants - when equilibrium is reached on the left side there are more reactants molecules, suggesting reverse reaction is more successful.

-Favours the products - when equilibrium is reached on the right side, there are more product molecules, indicating that forward reaction is favoured.

What do the reversible arrows suggest at a state of equilibrium?

• reactant and product concentration remain constant

what happens the closer a forward or reverse reaction reaches dynamic equilibrium?

• decreases