Chemistry 12 - Equilibrium

What does spontaneously reversible mean?

The rev Ea is low enough to happen often

What makes the rev rxn impossible?

The rev Ea is too high

What are examples of an impossible rev rxn?

Burning wood, cooking food, rust, rotting food, digestion

What is dynamic equilibrium?

Fwd and rev reactions are happening at the same time

What is happening on the macro and microscopic level during equilibrium?

Nothing happens at the macroscopic level, but changes are occuring at the microscopic level

What happens to the concentrations during equilibrium?

They are unchanged once the rxn reaches equilibrium

What are the three types of equilibrium?

Phase, solubility, and chemical

What is chemical equilibrium?

When reactants are being converted into products and products are being converted into reactants at the same time in a closed system

What are two conditions that affect equilibrium?

Open container and temperature

What are three conditions that are required for a system to reach equilibrium?

Reversible reaction, closed system, constant temp/pressure

What is enthalpy?

The heat content of a system, or chemical PE

In an exothermic reaction, what is the sign of enthalpy and is it increasing or decreasing?

Negative, the enthalpy is decreasing

In an endothermic reaction, what is the sign of enthalpy and is it increasing or decreasing?

Positive, the enthalpy is increasing

Will a chemical reaction favour the side with minimum or maximum enthalpy if no other factors are considered?

It will favour the side with minimum enthalpy, lower PE

If the reaction is exothermic, do the products or reactants have minimum enthalpy, and is the formation or reactants or products favourable?

The products have minimum enthalpy and the formation of products is favourable

If the reaction is endothermic, do the products or reactants have minimum enthalpy, and is the formation or reactants or products favourable?

The reactants have minimum enthalpy and the formation of reactants is favourable

what does entropy mean?

Disorder or lack of order

What state has the greatest entropy?

Solid, then liquid, then aqueous, then gas has the greatest

How do you tell if reactants or products have maximum entropy?

The side with the gases or more moles

Solids<liquids<aqueous<gas<more moles

Does nature favour minimum or maximum entropy?

There is a tendency in nature towards maximum entropy/disorder

Which side will the reaction favour, in terms of enthalpy and entropy?

Maximum entropy and minimum enthalpy

What happens when entropy and enthalpy favour the same side, or favour opposite sides?

If reactants are unanimously favoured, the reaction will not proceed

If the products are unanimously favoured, the reaction will go to completion

When the two disagree, the reaction will reach equilibrium

What is Le Chatelier’s Principle?

If a closed system at equilibrium was subjected to a change, processes will occur that tend to counteract that change (equilibrium will shift to the left or right)

If you add heat to a system, which way will it shift?

It will shift in a way that tends to use up the added, heat

When the temperature is increased, the equilibrium will shift away from the side with the heat term

If you remove heat from a system, which way will it shift?

It will shift in a way that tends to produce heat

When the temperature is decreased, the equilibrium will shift toward the side with the heat term

What is partial pressure of a gas?

The pressure exerted by one gas in a mixture of gases, where the more gas you have, the greater it's partial pressure

Another way of saying concentration

If you increase the concentration of a certain substance in an equilibrium mixture, which way will the reaction shift?

The system will shift so as to reduce the concentration of that substance

If you decrease the concentration of a certain substance in an equilibrium mixture, which way will the reaction shift?

The system will shift so as to increase the concentration of that substance

Is the relationship between volume and pressure directly or inversely related?

Inversely

Volume increased, pressure decreased

Volume decreased, pressure increased

Is the relationship between moles of gas and pressure directly or inversely related?

Directly

Moles increased, pressure increased

Moles decreased, pressure decreased

What does it mean if all substances spike/dip on a graph?

There was a change in volume or total pressure

When the total pressure is increased in an equilibrium system with gases, which way will the reaction shift?

The system will shift towards the side with less moles of gas in the equation

When the total pressure is decreased in an equilibrium system with gases, which way will the reaction shift?

The system will shift to the side with more moles of gas in the equation

What affect will the addition of an inert/unreactive gas to equilibrium?

It will not affect concentrations of reactants or products and will not cause a shift

What affect does adding a catalyst to a system not at equilibrium do?

It will simply speed things up so that equilibrium is attained faster

What affect does adding a catalyst to a system not at equilibrium have?

Both fwd and rev rxn rates increase but there is no change in equilibrium

What is Keq?

The equilibrium constant

What is the Keq expression?

The concentration of products over the concentration of reactants

What is the only thing that can change the value of Keq?

Temperature

What are the three rules of writing a Keq expression?

Liquids and solids aren’t included because they have a fixed concentration

The # of moles/coefficient becomes the exponent

Products over reactants

When the temperature is increased in an endothermic reaction, where will the equilibrium shift and what will happen to the Keq?

The equilibrium will shift to the right and the value of Keq will increase

When the temperature is decreased in an endothermic reaction, which way will the equilibrium shift and what will happen to the Keq?

The equilibrium will shift to the left and the Keq will decrease

When the temperature is increased in an exothermic reaction, which way will the equilibrium shift and what will happen to the Keq?

The equilibrium will shift to the right and the value of Keq will decrease

When the temperature is decreased in an exothermic reaction, which way will the equilibrium shift and what will happen to the Keq?

The equilibrium will shift to the right and the value of Keq will increase

What is the Keq equation of the reverse reaction?

The reciprocal of the Keq of the forward reaction

How do you solve for Keq at equilibrium when you are given concentrations of all species at equilibrium?

Write out the Keq expression, plug in the values for the equilibrium concentrations, and calculate

How do you solve for Keq at equilibrium or concentrations of all species at equilibrium when given initial concentrations of all species and equilibrium concentrations of one species

Make an ice table (initial, change, equilibrium), figure out the change for one molecule and use mol ratio to figure out change for all molecules, solve

How do you solve for Q when given initial concentrations of all species and Keq?

Set up the Q expression (same as Keq expression but with initial concentrations), and compare Q with Keq

When Q is less than Keq, which way will the system shift?

Right

When Q is greater than Keq, which way will the system shift?

Left

How do you solve for equilibrium concentrations of each special when given only initial concentrations and a Keq?

Determine how the equilibrium will shift by solving for Q, then use x as a variable in the C row of the ICE table, sub in values into the Keq expression and solve for x, sub in x to calculate the concentrations of each species