Unit 8A Flashcards
Rate
Change that occurs within an interval of time
Reaction rate
The changing reactants to products (or the reverse) per unit of time
Reversible reactions
A reaction that can move in both the forward and reverse directions
In a chemical equation, a double sided arrow is used to represent a reversible reaction in the balanced equation
Forward reaction
When reactants convert to products
Reverse reaction
When products reform reactants
STUDY ENERGY DIAGRAMS P1 OF NOTES
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Activation energy
The minimum amount of energy required in order to get a reaction started (to get to the top of the hill)
Can be calculated for both forward and reverse reactions
Activated complex/transition state
Can be found at the peak of the energy diagram. A temporary arrangement formed by the reactants, where they have enough energy to form products OR go in the reverse direction and reform reactants.
Endothermic
Reactions that require an input of energy to occur ex photosynthesis
Exothermic
Reactions that release energy ex combustion
Enthalpy
Change in heat energy (products-reactants)
Collision theory
For a reaction to occur it is necessary for the reacting species (atoms or molecules) to come together or collide with one another. Not all collisions, however, bring about chemical change.
To be effective, particles must collide with enough kinetic energy AND must collide in the proper orientation.
Factors affecting reaction rates
Temperature, concentration, particle size, catalyst
Temperature
Generally, an increase in temperature increases reaction rates, while a decrease slows a reaction down.
Increasing temp speeds up particles, increasing kinetic energy
Concentration
In a given volume, the number of particles affects the rate of reaction. Increasing the number of particles increases the concentration and the reaction rate.
More particles will increase the reaction rate
Particle size
The smaller the particles, the greater the surface area for a given mass of particles. An increase in surface area increases the rate of reaction.
With more exposed area to react, this increases the rate of reaction
Catalyst
Any substance that increases the rate of a reaction without being consumed
Catalysts allow reactions to proceed by lowering the activation energy.
Ex human enzymes
Chemical equilibrium
The state at which the forward and reverse reactions take place at the same rate
Difference between rate and concentration
Although the rates of the forward and reverse reactions are equal at chemical equilibrium, the concentrations are not necessarily the same
Favored
The thing with the higher concentration is favored
Catalysts
Although catalysts speed up a reaction rate, they will not affect the concentration of reactants and products present at equilibrium
They simply decrease the time it takes to establish equilibrium
Le Châtelier’s principle
When a stress is applied to a system at equilibrium, the equilibrium will shift in order to relieve stress
Factors affecting equilibrium
Concentration, temperature, pressure/volume
Concentration
Changing the amount, or concentration, of any reactant or product in a system at equilibrium disturbs the equilibrium
Adding a product shifts equilibrium to left, products will decrease, reactants increase
Adding reactant shifts to right, products increase, reactants decrease
Temperature
Increasing the temperature causes the equilibrium position of a reaction to shift in the direction that will absorb heat
Adding heat shifts to left
Taking away heat shifts to right
Pressure/volume
Changing pressure only affects an equilibrium with an uneven number of reactants and products (gas phase)
Increasing pressure will shift the equilibrium in the direction of the least amount of number of molecules of gas
Change in volume is a change in pressure
Reducing volume will increase pressure, and vice versa
Increasing pressure will shift equilibrium to side with less moles, vice versa
Equilibrium constant expressions
Can be used to determine whether products or reactants are favored in a chemical equilibrium
Steps for determining Keq
Cross off any reactants or products that are in the solid or liquid state
Write the product in the numerator, using brackets (which represent concentration) to separate them if there is more than one
Write the reactant in the denominator, using brackets if there is more than one
Raise each substance’s concentration to the power equal to the substance’s coefficient in the balanced chemical equation
General Keq formula for aA + bB cC + dD
Keq = ((C)^c (D)^d)/((A)^a (B)^b)
If Keq is very…
High
Low
Close to one
Products favored
Reactants favored
Roughly equal amounts of products and reactant present at equilibrium
