Chemistry Equilibrium and Solutions Test

What is equilibrium?

when the identity of something changes but the amount stays the same

Chemical Equilibrium

dynamic system in which the concentration of all reactants and products remain constant over time, indicated by a double sided arrow

What needs to happen in order for reactants to become products and products to become reactants?

the rate of the forward reaction and reverse reaction need to be equal

Phase Equilibrium

when a substance is at a temperature and pressure where it can change phase, the two phases exist in equilibrium during that change

Solution Equilibrium

in a saturated solution where there is excess solute on the bottom of the container, some particles in the solution will precipitate while solid particles dissolved

What are the three ways to disrupt equilibrium?

1. Change the concentration: add or take away reactants or products

2. Change the pressure: This will only affect equilibrium on a system that contains gases

3. Change the temperature: make it warmer or colder

What will you need to know when discussing equilibrium stresses?

the sign of ΔH of the reaction

What will a reaction do after being disrupted by Le-Chatlier’s Principles?

try to shift itself to get back to equilibrium

How do you remember which way to shift the reaction after it’s been disrupted by Le-Chatlier’s Principles?

Add away, take towards

(add—> increase, away)

(take—> decrease, toward)

How does changing concentration through Le-Chatlier’s principle change a reaction?

if there is more of something on one side than the other, say reactants, then the concentrations are out of balance, so the reaction works to make the two sides equal

What happens when a reactant’s concentration in increased (Le Chatlier’s Principle)?

The reaction will shift right (away) to make more product (shift right)

What happens when a product’s concentration is decreased (Le Chatlier’s Principle)?

the reaction will shift left (towards) to make more reactants

How does changing the pressure change a reaction?

the equilibrium will shift to get the pressure back to normal

More moles of gas has a larger ______ and exerts more ______

volume, pressure

Which way does a reaction shift to get equilibrium back when pressure is increased (or when volume is decreased)?

the reaction shifts to the side with fewer moles of gas (shifts right)

Which way does a reaction shift to get equilibrium back when pressure is decreased (or when volume is increased)?

the reaction will shift towards the side with more moles of gas to try to get the pressure back (Shift left)

What happens when there are the same number (concentration) of moles on each side of the reaction?

there is no effect

Increasing temperature favors the ______ reaction

endothermic

Why does increasing temperature favor the endothermic reaction?

because the reaction is trying to absorb energy

Decreasing temperature favors the ______ reaction

exothermic

Why does decreasing temperature favor the exothermic reaction?

because the reaction is trying to release energy

Which way does a reaction shift when temperature is increased?

shifts right

Which way does a reaction shift when temperature is decreased (exothermic reaction)?

shifts left

Solution

a homogeneous mixture in the same physical state

Solute

the substance that is being dissolved, usually something ionic

Solvent

the substance that does the dissolving (usually water)

Homogeneous Mixture

a mixture in which the particles are uniformly mixed, looks the same throughout

Aqueous

dissolved in water; a homogeneous mixture where water is one of the components

Soluble

substance that dissolves well

Insoluble

substance that is not dissolve-able

Concentration

a measure of the amount of a substance mixed with a second substance

Concentrated

a relative term for a solution having a large amount of a substance dissolved in a second substance

Dilute

relative term for a solution that has a small amount of a substance dissolved in a second substance

Saturated

solution containing the maximum amount of solute that will dissolve at a given temperature, solid begins to accumulate on the bottom of the container

Unsaturated

a solution that can dissolve more solute at the given temperature

Super saturated

a solution that contains more solute than should dissolve in a saturated at a given temperature, prone to rapid crystallization

Precipitate

the insoluble product of a reaction between 2 aqueous solutions

a solid that comes out of a solution as a result of a chemical reaction or drop in temperature

Dissociation

Ions breaking apart upon dissolved in water by the molecule-ion effect

Percent Composition by Mass

the concentration of a solution expressed as the ratio between the mass of the solute and the total mass of the compound

how much solute is in the solvent with respect to mass expressed as a percent

Percent Composition by Volume

the concentration of solution expressed as the ratio between the volume of the solute and the total volume of the solution expressed as a percent

how much solute is in the solvent with respect to volume (usually liquid dissolved in liquid) expressed as a percent

Parts Per Million

the ratio between parts of solute per million parts of the solution

Le Chatlier’s Principle

a system in equilibrium will react to reduce a stress

Molarity

the concentration of a substance in moles per liter of a solution

how many moles of a solute is in liters of a solution. Never represented as a fraction

Colligative Properties

Changes to physical properties of boiling point, vapor pressure, surface tension, osmotic pressure, and freezing point due to adding a solute to a solvent

Molecule-Ion Effect

molecules that have partial charges can attract the full charges on ions

*only for ionic substances

What is known as the universal solvent?

water

What makes water a universal solvent?

it’s polar (asymmetrical) so water uses its partial charges to break apart the crystal lattice (dissolving)

What is dissolving?

when a solvent (usually water) uses its partial charges to break apart the crystal lattice

What happens in dissociation?

the negative end of water (oxygen) is attracted to the positive ion, and pulls it away from the negative ion. The reverse is true as well.

What is the result of dissaciation? What does this create due to mobile ions?

an aqueous solution

this creates an electrolyte once mobile ions are added

Electrolyte

a solution that conducts electricity

Acids will or will not dissolve in water, even though they are covalent.

will

Why don’t covalent substances have the same type of response when mixed with water?

because they aren’t made of ions that can be pulled apart by water

How do polar covalent substances react with water? What about nonpolar covalent substances?

Polar covalent— usually dissolve to a small degree

Nonpolar covalent—struggle to have even a small amount of dissolving

What kinds of solvents and solutes can go together (composition)?

Polar solutes and polar solvents

Nonpolar solutes and nonpolar solvents

Don’t mix and match them

Dissolving Solids

when solids dissolve in a liquid (usually water) the water molecules need to move out of the way to make room for the solid to dissociate and dissolve

How can you aid solids in dissolving?

1. increase temperature

2. stir or agitate

3. low concentration

4. high surface area (crushed)

Dissolving Gases

when gases dissolve in a liquid (usually water) the water molecules need to stay close together to ensure the gas bubbles don’t rise and escape

How can you aid gases in dissolving?

1. decrease temperature

2. don’t stir or agitate

3. high pressure (squeeze bubbles down)

Does a substance with ionic bonds or that are polar always have to dissolve?

no, they are not guaranteed to dissolve in water

Double Replacement

positive and negative ions swap partners

Precipitation Reaction

one of the products of a double replacement is a precipitate (solid)

What does it mean if both products are aqueous?

no reaction has occurred

When can a precipitation reaction take place?

This reaction will only take place if the two reactants are soluble because there is no other way to get the ions to dissociate and swap partners

Only one product should be soluble, because if both were, no reaction would really occur since the ions will just float around

What happens in a drawing of a precipitate reaction on the reactants side?

reactants dissolve and dissociate (each ion floats around separately)

What happens in a drawing of a precipitate reaction on the products side?

extra ions float around (spectator ions, ones that are aqueous) and one insoluble product is formed (solid is put together on bottom of the container)

How can you separate the product of a precipitation reaction?

Filter to remove the precipitate, evaporate to remove water and dry up dissolved ions

The terms dilute and concentrated are _________ and relative terms.

qualitative (no numeric values)

What are the four different ways you can determine how much solute is dissolved in the solvent?

1. percent by mass

2. percent by volume

3. parts per million

4. molarity

What is the percent by mass equation?

(mass of solute/mass of solution) x 100

What is a solution composed of?

solute and solvent

What is the equation for percent by volume?

(volume solute/volume solution) x 100

Parts Per Million

how much solute is in the solvent with respect to mass expressed out of one million

Parts Per Million Equation

(mass of solute/mass of solution) x 10⁶

Molarity Equation

moles of solute/liters of solution

What are the units for molarity?

mol/L or molar (M)

What is molarity used for? Why?

preparing solutions for chemical reactions because in a balanced chemical equation, the coefficients represent moles

In what unit are solutions usually measured in?

volume, not mass

What are the steps to making a solution with a particular molarity or concentration?

1. determine the number of moles of solute you’ll need

2. determine the number of grams you’ll need to measure

3. add solid to the bottom of a volumetric flask

4. fill to the line. Be very careful not to go over. Overfilling the flask will dilute the solution

Stoichiometry

the relationship between the quantities of reactants and products before, during, and after chemical reactions

When working with solutions, what do coefficients of a balanced equation represent?

moles

How do you figure out the number of moles in a sample given the volume? In what instances can you do this?

use the molarity equation

you can do this when you know the concentration of the solution and volume used to determine the number of moles

Solution equilibrium occurs in solutions that are in what state?

saturated

A bottle contains water. How can phase equilibrium be reached?

if the bottle is sealed so that vapor can’t escape

In order for a reaction to be in a state of equilibrium, what must be true?

the rates must be equal resulting in the concentrations of reactants and products remaining constant

What would happen to equilibrium if a catalyst was introduced into a reaction?

the reaction may reach equilibrium more quickly

How does introducing a catalyst impact Le Chatlier’s Principle?

no effect

Which way does reducing the volume of a reaction vessel shift for equilibrium?

right

Which way does increasing the volume of a reaction vessel shift for equilibrium?

left

Which way does increasing temperature shift for equilibrium?

right

Which way does decreasing temperature shift for equilibrium?

left

What must you consider when determining whether a compound will dissolve in water?

bond type (whether its covalent or ionic) and shape (whether its polar or nonpolar)

What determines how fast a substance will dissolve?

solubility and conditions (like temperature, pressure, etc)

Why does the dissolved component not settle out of the solution (not sink to the bottom)?

because the compounds break into ions that are attracted to water. Ions need to be paired with opposite charges, they can’t exist on their own