Lesson 12.3: Reversible Reactions and Equilibrium

​Lesson 12.3: Reversible Reactions and Equilibrium

Multiple Choice

What name is given to the minimum amount of energy needed by particles for them to react when they collide?

• Activation energy

• Catalytic energy

• Threshold energy

Multiple Choice

which factor that affects reaction rate is represented in the picture?

• Temperature

• Catalyst

• Surface Area

• Concentration

Multiple Choice

Which of these will NOT speed up the rate of reaction between a strip of magnesium and hydrochloric acid?

• roll the magnesium strip into a small ball

• Grind up the strip of magnesium

• increase the concentration of the hydrocholoric acid

• increase the temperature of the hydrocholoric acid

Multiple Choice

A ______________ is a substance that increases the rate of a reaction without being used up during the reaction. 

• catalyst

• product

• reactant

• solute

Multiple Choice

B represents

• Potential Energy of Products

• Potential Energy of Reactants

• Change in Enthalpy

• Activation Energy

​Reversible Reactions

• Reactions involve an interaction where a reactant undergo a change from reactant to a product

• Reversible Reactions: Reactions where product molecules under ordinary conditions can react to form the original reactant molecule

  • Shown with a double arrow (↔)

  • Some favor products, some favor reactants

    • Side that is favored has a bigger side to their arrow

  • All aspects of the reaction are reversed

    • If exothermic in one direction, it is endothermic in the other direction

Experience Chemistry | Lesson 12.3

​Chemical Equilibrium

• Chemical Equilibrium: a state of balance in which the rates of both the forward and reverse reactions are equal

  • Both reactions happen at the same rate at the same time, so there is no noticeable change in the concentrations

• Equilibrium Position: the relative concentrations of the reactants and products at equilibrium

  • What the Equilibrium concentrations are

Experience Chemistry | Lesson 12.3

​Le Châtelier's Priniciple

• Usually reaction systems change from being out of equilibrium into equilibrium, but sometimes outside forces can alter a system already in Equilibrium

• Le Châ​telier's Principle: if a chemical system at equilibrium experiences a disturbance, it changes in a way that returns the system to equilibrium.

Experience Chemistry | Lesson 12.3

​Le Châtelier's Principle Concentration Example

• The reversible reaction of Carbon dioxide and carbonic acid takes place in your body: CO₂ + H₂O ↔ H₂CO₃

  • When you exercise, your body produces more carbon dioxide through cellular respiration.

    • To avoid Hypercapnia, your body converts the CO₂ to H₂CO₃

  • When too much H₂CO₃ builds up, your body is triggered into breathing heavily and removing CO₂, Forcing your body to break down the H₂CO₃ to CO₂ and return to equilibrium

Experience Chemistry | Lesson 12.3

​Le Châtelier's Principle Pressure Example

• Hydrogen Sulfide gas is formed from hydrogen gas and sulfur gas in the following reversible reaction: 2 H₂ + S₂ ↔ 2 H₂S

  • When kept in a container where the pressure increases, there is less room for molecules to move around, so the product is favored

  • When kept in a container​ where the pressure decreases, there is more room, so the reactants are favored

Experience Chemistry | Lesson 12.3

​Le Châtelier's Principle Temperature Example

• Ammonia gas is formed from nitrogen gas and hydrogen gas in the exothermic reaction: N₂ + 3H₂ ↔ 2NH₃ + heat

  • When you raise the temperature, there is excess heat (a product), so reactants are favored

  • If you decrease the temperature, there is a deficit of heat, so products are favored

Experience Chemistry | Lesson 12.3

Multiple Choice

If a reversible reaction is exothermic in the forward direction, it will be ...

• exothermic in the reverse direction

• endothermic in the forward direction too

• endothermic in the reverse direction

• not involve energy in reverse direction

Multiple Choice

Consider the reaction: H₂O₂ ↔ H₂ + O₂

It has a ΔH of 187 kJ/mol.

Is the reaction an exothermic or endothermic reaction?

• Exothermic

• Endothermic

Multiple Choice

Consider the reaction: H₂O₂ ↔ H₂ + O₂

It has a ΔH of 187 kJ/mol.

If you add H₂ to the system, which side of the reaction is favored?

• Reactants

• Products

Multiple Choice

Consider the reaction: H₂O₂ ↔ H₂ + O₂

It has a ΔH of 187 kJ/mol.

If you remove O₂ from the system, which side of the reaction is favored?

• Reactants

• Products

Multiple Choice

True or false: Once a reaction is in equilibrium, it can never be changed out of Equilibrium

• True

• False