Unit 3: Chemical Equilibrium Flashcards
Can chemical reactions be undone?
Under the right conditions, they can be undone.
What is the “right condition” for most reactions to reverse?
Most reactions are exothermic, meaning that they release energy (energy is removed from the system, negative delta H). So, energy or a catalyst are needed to reverse a reaction (refer to graph in notes)
What is notable about equilibrium reaction equations?
They have a double arrow between the products and reactants.
What is equilibrium?
Chemical equilibrium is when the forward and reverse reactions are proceeding at the same rate.
It occurs in a closed system (no matter can enter or leave).
No observable changes (the microscopic level is still active).
Two types of equilibrium (phase and dynamic).
What is phase equilibrium?
A balance between two phases of matter (like solid and liquid). Refer to the sealed soda container example.
What is dynamic equilibrium?
A balance between forward and reverse chemical reactions. The products become the reactants as the reactants become the products.
What is Le Chatelier’s Principle?
If stress is applied to a system at equilibrium, a temporary non-equilibrium state will occur. The system will then shift in the direction opposite to the change (returning to equilibrium). There are three stresses that may affect an equilibrium rate: change in concentration, change in volume, and change in temperature.
How does a change in concentration affect equilibrium?
The system will react to replace a removed substance or use up an added substance.
How does a change in volume or pressure affect equilibrium?
This only affects gasses. Gasses take up the volume that they are in. If volume is increased (pressure decreased), the equilibrium favours the direction that produces more moles of gas. If the volume is decreased (pressure increased) the equilibrium favours the direction that produces fewer moles of gas.
How does a change in temperature affect equilibrium?
Every equilibrium has both an exothermic and an endothermic direction. If you add heat, the reaction favours the endothermic reaction (the endothermic reaction removes heat). If you remove heat, the reaction favours the exothermic reaction (releases more heat).
What does keq represent?
The equilibrium constant.
What represents the equilibrium constant?
Keq.
What is keq/the equilibrium constant?
A numerical value (no units) that describes the system once it has reached equilibrium. Keq > 1, products favoured. Keq < 1, reactants favoured.
What is the keq expresssion?
keq = ([C]^c * [D]^d) / ([A]^a * [B]^b) where aA + bB <-> cC + dD
Capitals are substances, lowercases are coefficients/amount. Do not include solids or pure liquids, only include gasses (gasses and non-pure liquids have concentration).
The product of the concentration of the products to the power of their amounts divided by the product of the concentration of the reactants to the power of their amounts.
What is the product and reactant in an equilibrium expression?
The reactants are always on the left. The reactants are always on the right.
What represents the reaction quotient?
Q
What does Q represent?
The reaction quotient.
What is the reaction quotient?
Like keq, Q is a ratio of the products to reactants. Calculated using instantaneous concentrations. If Q = keq, the reaction is at equilibrium. If not, then you can determine which way the reaction should shift. If Q<Keq, system has more reactants than at equilibrium, so it will move in the forward direction. If Q>Keq, there are more products than at equilibrium, so it will move in the reverse direction.
What does I.C.E. stand for?
I: Initial or instantaneous concentrations.
C: Change in concentration.
E: Equilibrium concentration.
How do I.C.E. calculations work?
Refer to charts and notes
What is solubility?
A measure of the maximum amount of substance that can dissolve in a given amount of solvent
What does it mean when a solution is saturated
The maximum amount of substance has been dissolved
What is a solute
What is being dissolved
What is a solvent
What the solute is being dissolved into
What is concentration
A measure of the solute per unit of the solvent C=solute/solvent or C=mol/L
What does of mean when something is saturated
The solution has a large amount of solute dissolved in it
What does it mean when something is dilute
It has a small amount of solute
What does it mean when something is unsaturated
The solution can hold more solute
What does it mean when something is supersaturated
The solution is holding more solute than it theoretically can at that temperature
What is an alloy
A solution of a metal in another metal
What axiom do chemists use to determine whether a solute will dissolve into a solvent?
Like dissolves like
Polar solutes tend to dissolve well in polar solvents
Non-polar solutes tend to dissolve well in non-polar solvents
Why are organic alcohols such great solvents?
They have polar and non-polar properties
Why does vitamin a dissolve into fat?
They are both non-polar
Why does vitamin c dissolve into water
They are both polar
What is dissociation?
Ionic compounds, when dissolving in water, break apart into their ions
AnBm(s) <-> NA(aq) + MB(aq)
What is ionization?
Dissociation, but with acids. The reactant is a liquid
What are electrolytes
Ionic or acidic compounds dissolved in water (they are free to move and they conduct electricity)
How do molecular compounds dissolve?
They do not ionize or dissociate, so they do not produce mobile ions
They are non-electrolytes (CO2) for example
What is solubility
The maximum amount of solute that will dissolve in a given amount of solvent
What factors affect solubility rates?
Surface area: more surface area speeds up dissolving
Agitation/stirring: Lets solvent particles collide with solute particles more often, speeding up dissolving (collision theory)
Temperature: Kinetic energy of particles increases (collision theory)
Does increasing temperature increase solubility?
In most cases, yes. Gasses especially decrease in solubility as temperature increases.
Conversion of grams and millilitres of water
1g water = 1ml water
How much of a solute must dissolve in a solvent for it to be considered soluble?
Usually,
More than 1g dissolves in 1L: soluble
Less than 1g dissolves in 1L: Insoluble
Steps to write a net ionic equation
Complete and balance reaction normally, including all states of matter (don’t break apart aqueous chemicals yet)
TI: write all (both sides) aqueous compounds as separate ions
NI: cancel ions that appear as both reactants and products, write what remains
What is ksp?
Solubility product constant. Describes how well a substance dissolves as a ratio of products to reactants.
ksp>1 dissolves well
ksp<1 dissolves poorly
How do you use ksp to determine whether a precipitate will form?
ksp presents the maximum amount of ions that will dissolve in solution
If Q>ksp: precipitate
If Q<ksp: no precipitate
Who proposed ionization and dissociation?
Svante Arrhenius
What is wrong with Cl2^-1 (aq)?
Diatomic elements share electrons and do not possess a charge. Ex: MgCl2(s) <-> Mg+2(aq) + 2Cl-1(aq).
