PAGE 16 — Equilibrium & Catalysts & PAGE 17 — Water & Solution

What is a catalyst?

A substance that speeds up a chemical reaction without being used up.

What is a biological catalyst called?

An enzyme

How does a catalyst speed up a reaction?

By lowering activation energy.

What happens to activation energy when a catalyst is added?

It decreases.

What happens to reaction rate when activation energy decreases?

The reaction happens faster.

Does a catalyst get consumed in a reaction?

No, it is not used up

Does a catalyst change the amount of product formed?

No, it only changes the speed

Does a catalyst change the energy released or absorbed?

No, only the pathway and rate.

Do both endothermic and exothermic reactions use catalysts?

Yes, all reactions can use catalysts

What do catalysts do to the energy diagram?

They lower the peak (activation energy).

What is a biological catalyst called?

An enzyme.

What does an enzyme do?

Speeds up reactions in the body by lowering activation energy.

What are factors that affect reaction rate?

• Concentration

• Surface Area

• Temperature

When concentration increases, what happens to reaction rate?

Increases the number of collisions between those reactants and therefore increases the reaction rate.

When surface area increases, what happens to reaction rate?

Increases the number of collisions between those reactants and therefore increases the reaction rate.

When temperature increases, what happens to reaction rate?

Increases the number of collisions but more significantly also increases the kinetic energy of the reactants, which in turn increases the fraction of molecules meeting the activation energy requirement.

What is chemical equilibrium?

When the forward and reverse reaction rates are equal.

What is a foward reaction rate?

How fast reactants turn into products.

What is a reverse reaction rate?

How fast products turn back into reactants

At equilibrium are the amounts of reactants and products equal?

The amounts of reactants and products are constant, not equal. What is equal are the forward and reverse reaction rates.

Is equilibrium a static or dynamic process?

Dynamic

• reactions continue in both directions at equal states

What is equal at equilibrium?

The foward and reverse reaction rates

Why do concentrations stay constant equlibrium?

Because both reactions occur at the same speed, so nothing changes overall

What type of system is required for equilibrium?

A closed system, where nothing enters or leaves and no heat is added or lost.

What is Le Châtelier’s principle?

When a system at equilibrium is stressed, it shifts to counteract the stress.

If concentration of a reactant increases which way does equilibrium shift?

Toward products

• shifts right

If concentration of a product increases which way does equilibrium shift?

Toward reactants

• shifts left

If temperature increases in an endothermic reaction which way does equilibrium shift?

Toward products (heat acts like a reactant)

• shifts right

If temperature increases in an exothermic reaction which way does equilibrium shift?

Toward reactants (heat acts like a product)

• shifts left

What does adding a catalyst do to equilibrium?

Nothing

• it only speeds up reaching equilibrium.

If pressure increases (or volume decreases) which way does equilibrium shift?

Toward the side with fewer gas molecules.

If pressure decreases (or volume increases) which way does equilibrium shift?

Toward the side with more gas molecules.

When does pressure affect equilibrium?

Only when the number of gas moles differs on each side

Does pressure affect equilibrium when both sides have the same number of gas moles?

No

• If the reactants and products have the same number of gas molecules, a pressure change causes no shift in equilibrium.

Does pressure affect equilibrium when no gasses are present?

No. Pressure changes only affect equilibria that involve gases.

• gas is compressible, solids and liquids arent

What stays equal at equilibrium: rates or amounts?

Rates

What stays constant at equilibrium: rates or concentrations?

Concentrations

Does equilibrium mean the reaction stops?

No, it continues in both directions

What happens if you remove reactant?

The reaction shifts toward reactants to replace it

• shifts left

What happens if you remove product?

The reaction shifts toward products to replace it

• shifts right

If temperature decreases in an endothermic reaction which way does it shift?

Toward reactants.

If temperature decreases in an exothermic reaction which way does it shift?

Toward products.

Why is water a polar molecule?

Because electrons are shared unequally between oxygen and hydrogen.

Which atom in water is more electronegative?

Oxygen.

What partial charge does oxygen have in water?

Partial negative (δ−).

What partial charge do the hydrogens have in water?

Partial positive (δ+).

What shape is a water molecule?

Bent (V‑shaped).

How does water’s shape affect polarity?

The bent shape prevents dipoles from canceling, making water polar

What type of bond forms between water molecules?

Hydrogen bonds.

Why can water dissolve many substances?

Because it is polar (“like dissolves like”).

Do polar molecules dissolve in water?

Yes.

Do nonpolar molecules dissolve in water?

No.

What is a solvent?

The substance that does the dissolving in a solution.

What is a solute?

The substance that gets dissolved.

In salt water what is the solvent?

Water.

In salt water what is the solute?

Salt.

Which is present in a larger amount: solvent or solute?

Solvent.

Which is present in a smaller amount: solvent or solute?

Solute.

What phrase helps remember solvent vs solute?

Solvent dissolves, solute gets dissolved.

What type of solvent is water?

A universal solvent.

Why is water a good solvent?

Because it is polar and forms hydrogen bonds, allowing it to dissolve ions and polar molecules.

What does cohesion mean?

Water molecules stick to each other due to hydrogen bonding.

What does adhesion mean?

Water molecules stick to other substances; hydrophilic substances attract water.

Why does water resist temperature change?

It has high specific heat because hydrogen bonds resist breaking.

Why does sweating cool the body?

Water has a high heat of vaporization, so evaporation absorbs heat.

Why does ice float?

Hydrogen bonds spread molecules apart, making solid water less dense.

What is a hydrogen bond?

A weak attraction between hydrogen and an electronegative atom (O, N, F).

Are hydrogen bonds strong or weak?

Weak, short‑lived, but numerous.

What gives water most of its special properties?

Hydrogen Bonding

What type of electromagnetic wave is UV radiation?

A high‑energy electromagnetic wave.

Where does UV radiation fall on the EM spectrum?

Between visible light and X‑rays

Does UV radiation have high or low energy?

High Energy

What can UV radiation cause in molecules?

It can break chemical bonds