Unit 2 CHEM - Exam Prep.

What is happening at **chemical equilibrium**?

The forward reaction and reverse reaction occur at the same rate.

What happens to the **concentrations** of products and reactants after reaching chemical equilibrium?

The concentrations stay **constant**.

What is **dynamic equilibrium**? Can we **see** the changes? Is there a change in **concentrations**?

A chemical system that is changing at the **molecular level**, while the **macroscopic properties** stay constant.

No changes are visible to the human eye, but the compounds involved are alternating constantly. The equilibrium stays **balanced** throughout the changes.

What **factors** must be present for **equilibrium**? (x6)

1. Closed system
2. Equality between the forward and reverse reaction rates.
3. Same equilibrium states are obtainable starting from either the reactant or product side.
4. Constant:
* Concentrations of reactants and products
* Temperature
* Pressure
* Colour
* pH

What are the **two types** of equilibria?

Homogenous and heterogenous equilibria

What is **homogenous equilibrium**?

When all **states** in the reaction are the **same**.

What is **heterogenous equilibrium**?

When there are **different states** in a reaction.

Does equilibrium mean that the **concentrations** of reactants and products are equal?

**No**, it means that the transfer (forward and reverse reactions) allows for concentrations to remain constant.

What is **another name** for the 'Law of Chemical Equilibrium'?

Law of Mass Action

What is the **Law of Chemical Equilibrium**?

In a chemical system at equilibrium, there is a constant ratio between the concentrations of products and concentrations of reactants.

What is an equilibrium **constant**?

**Ratio of** __**equilibrium**__ **concentrations** foHr a particular chemical system at a certain temperature.

Does an equilibrium constant have a **unit**?

**No**, it’s unitless.

In the equilibrium constant expression are **all states included**?

**No**, only **gases** and **aqueous solutions**. Solids and liquids are excluded.

What does the equilibrium constant tell us?

K>1: product formation is favoured.

K=1: there is approx. equal product and reaction formation.

K

What is **Le Chatelier’s Principle**?

If an **external stress** is applied to a chemical system at equilibrium, the rates of the forward and reverse reactions are **temporarily unequal** because stress affects the reaction rates. However, equilibrium is **eventually restored**.

How do **concentration changes** impact equilibrium?

**Product:**

* Increase: shift to reactants.
* Decrease: shift to products.

**Reactant:**

* Increase: shift to products.
* Decrease: shift to reactants.

Which external stress factor impacts the equilibrium constant?

Only temperature.

How does **temperature** impact the equilibrium constant? Does it depend on the **type of reaction**?

**Endothermic**

* INCREASE: increase in equilibrium constant.

**Exothermic**

* INCREASE: decrease in equilibrium constant.

Do changes in **volume** and **pressure** impact the equilibrium constant?

No.

Do changes in **concentration** impact the equilibrium constant?

No.

Can pressure and volume impact a solid or liquid?

No, their volumes are constant and are almost incompressible.

What equilibrium system is affected by changes in pressure and concentration?

**Gaseous** systems.

What is the relationship between pressure and volume?

Inverse

What happens to the equilibrium system when there is an increase in pressure/decrease in volume?

Shift to the products, so that compounds are formed and there are less particles moving about.

What happens to the equilibrium system when there is a decrease in pressure/increase in volume?

Shift to the reactants, so that there are more particles moving about, filling the space.

What does the **number of moles** in a reaction tell you about how **pressure** impacts equilibrium?

When there’s an **increase** in pressure, equilibrium will **shift** **to** the side with a **total of fewer moles**. When the number of moles on both sides are equal, pressure has no effect.

Do **catalysts** have effects on equilibrium?

No, in neither direction.

What can the reaction quotient (Q) tell us?

Whether or not the reaction is at equilibrium.

Q>K: reaction will proceed in reverse direction to reach equilibrium because ratio of products to reactants is too large.

Q=K: system is at equilibrium.

Q

How do you determine the reaction quotient (Q)? What **expression**?

Same expression as equilibrium constant, however you’re using the initial concentrations.

What visual can we use when comparing the K and Q to find the direction the reaction must go in to return to equilibrium?

Number line. Place K and Q values, move from Q to K. That is the direction the reaction must go in.

What is **solubility equilibria**?

Dynamic equilibria between a solute and a solvent that occurs in a saturated solution. It has its own solubility product constant.

How do you find the **molar solubility**?

The **‘x’** of the ICE table.

How can you **quantitatively** determine is a precipitate forms?

With the comparison between Q and Ksp.

Qsp>Ksp: supersaturated solution, a precipitate will form.

Qsp=Ksp: saturated solution, a precipitate will form.

Qsp

Do the concentrations used to find Q have to be at equilibrium?

No, but they can be.

What is the **common ion effect**?

A **decrease in solubility** which occurs when an ionic compound is dissolved in a solution that contains an ion in common with the **solid**.

What is a **precipitate**?

An insoluble **solid** formed from a super-saturated aqueous solution.

What is the **strength** of an acid? (def.)

An acid’s ability to dissociate in a solution.

What is pH and pOH?

Measures of how acidic or basic a solution is.

**pH:** a measure of hydronium ions within a solution.

**pOH**: a measure of hydroxide ions within a solution.

What are the **Sig. Fig.** rules pH and pOH?

Number of Sig. Figs in the concentration are the number of decimal points for pH/pOH.

What are the differences in **taste** between acids and bases?

Acids: sour

Bases: bitter

What is the **Bronsted-Lowry Acids and Bases** theory?

Protons transfer from acid to base.

ACIDS: proton donors

BASES: proton acceptors

What is amphoteric vs. amphiprotic?

**Amphoteric:** Can act as an acid or a base.

**Amphiprotic:** more specific, can donate or accept a proton.

What are **acid-base conjugate pairs**?

Two species (acid and base) that differ by a **proton**.

* Acid: contains the proton.
* Base: lacks the proton.

Acid (had proton)→Conjugate Base (lost proton)

Base (lacked proton)→Conjugate Acid (gained proton)

What is the correlation between the strength of an acid and the strength of its conjugate base?

**Strong** acids=conjugate bases that are **poor** proton acceptors.

**Weak** acids=conjugate bases that are **good** proton acceptors.

What is special about the **rate of dissociation and formation** for **water**?

They’re **equal**; in the system of water molecules, hydronium ions and hydroxide ions are at **equilibrium**.

What is the Ion-product constant of water?

Kw=\[H30+\]\[OH-\]

=1.0x10^-14 (at 25 Deg. C)

* therefore: \[H3O+\]=\[OH-\]=1.0x10^-7

What is a **strong acid**?

Ionizes almost 100% in water.

What is **ionization**?

Splitting up of ions into new charged particles. **Irreversible**.

Are strong acids/bases at equilibrium? Why/why not?

No equilibrium. They go to completion.

Does the **strength** of an acid correlate to its level of **danger**? What does?

No, its concentration does.

What are **strong bases**?

Compounds that quantatively **produce hydroxide ions** in water.

What are **weak acids/bases**?

Acids/bases that **do not ionize/dissociate completely** in water.

What is **dissociation**?

Separation of charged particles. Is **reversible**.

Are the **initial** and **equilibrium** **concentrations** of weak acids equal?

Yes, approxiamtely because so few hydronium ions form.

What **direction** does an acid-base reaction shift in?

The direction in which the stronger acid and stronger base form a weaker acid and weaker base.

What is a **monoprotic** acid?

Possesses **one proton**/hydrogen ion.

What is the equilibrium constant for the ionization of an acid?

Ka, the acid ionization constant.

What are the relationships between the strength of an acid, its concentration of hydronium and its Ka value size?

The stronger an acid, the higher the hydronium ion concentration, and the larger the Ka value.

What is the equilibrium constant for a weak base?

Kb, the base ionization constant.

What is the relationship between the strength of a base and the size of its Kb?

Stronger bases=larger Kb

Weaker bases=smaller Kb

What is the strength of a weak acid’s conjugate base?

Weak

What is the strength of a very weak acids conjugate base?

Strong

What is a **neutralization** reaction?

When an acid and base react to form a salt and liquid water.