LE CHATELIER’S PRINCIPLE | Catalysts | Enzymes

What is a reversible reaction?

A reaction that proceeds in both forward and reverse directions.

What does the double arrow mean?

The reaction is reversible and can go forward and backward.

What is the forward reaction?

Reactants forming products.

What is the reverse reaction?

Products forming reactants.

What is chemical equilibrium?

A state where the forward and reverse reaction rates are equal.

At equilibrium do concentrations change?

No they remain constant.

Is equilibrium static or dynamic?

Dynamic because reactions continue in both directions.

What stays equal at equilibrium?

The rate of the forward reaction equals the rate of the reverse reaction.

What does Le Chatelier’s principle state?

A system under stress will shift to undo the stress and reestablish equilibrium.

What is a “system” in equilibrium?

All reactants and products together.

What are the main stressors that affect equilibrium?

Concentration heat and pressure/volume.

What does a shift to the right mean?

More products are formed.

What does a shift to the left mean?

More reactants are formed.

Which states affect equilibrium?

Gases (and aqueous) only.

Do solids affect equilibrium?

No solids do not affect equilibrium.

Do liquids affect equilibrium?

No liquids do not affect equilibrium.

If concentration of a reactant increases what happens?

The system shifts right to make more product.

If concentration of a reactant decreases what happens?

The system shifts left to make more reactant.

If concentration of a product increases what happens?

The system shifts left to make more reactant.

If concentration of a product decreases what happens?

The system shifts right to make more product.

Which states change equilibrium when concentration changes?

Gases (and aqueous species).

Where is heat written in an endothermic reaction?

On the reactant side.

Where is heat written in an exothermic reaction?

On the product side.

If heat is added to an endothermic reaction what happens?

The system shifts right.

If heat is removed from an endothermic reaction what happens?

The system shifts left.

If heat is added to an exothermic reaction what happens?

The system shifts left.

If heat is removed from an exothermic reaction what happens?

The system shifts right.

What must you identify before predicting heat shifts?

Whether the reaction is endothermic or exothermic.

When do pressure and volume affect equilibrium?

Only when gases are present.

How are pressure and volume related?

Inversely: increased volume lowers pressure and decreased volume raises pressure.

If pressure increases what happens?

The system shifts to the side with fewer moles of gas.

If pressure decreases what happens?

The system shifts to the side with more moles of gas.

What must you count to determine pressure shifts?

The moles of gas on each side of the equation.

What is reaction rate?

The change in concentration of reactants or products over time.

What must molecules do for a reaction to occur?

They must collide with enough energy and at the correct reactive site.

What is activation energy?

The minimum energy required to start a reaction.

How does activation energy affect reaction speed?

Lower activation energy makes reactions faster; higher activation energy makes reactions slower.

What is the reactive site?

The specific location on a molecule where a collision must occur for reaction.

How is activation energy different from reactive site?

Activation energy is required energy; reactive site is required location.

How does temperature affect reaction rate?

Higher temperature increases reaction rate.

Why does higher temperature increase reaction rate?

Molecules move faster collide more and have more energy.

How does concentration affect reaction rate?

Higher concentration increases reaction rate.

How does pressure affect reaction rate for gases?

Higher pressure increases reaction rate.

How does surface area affect reaction rate?

More surface area increases reaction rate.

What is a catalyst?

A substance that speeds up a reaction without being consumed.

How does a catalyst speed up a reaction?

By lowering activation energy.

Does a catalyst change reactants or products?

No it only changes the reaction pathway.

Does a catalyst get used up?

No catalysts are reusable.

What is a biological catalyst called?

An enzyme.

How does a catalyzed reaction look on an energy diagram?

It has a lower activation energy peak.

What does equilibrium describe?

Balance of concentrations and equal forward/reverse rates.

What does reaction rate describe?

How fast reactants turn into products.

How are equilibrium and reaction rate connected?

At equilibrium the forward and reverse rates are equal.

Does a catalyst change equilibrium position?

No it only helps the system reach equilibrium faster.