Unit 8 - Kinetics & Equilibrium - Regents Flashcards
Definition of Kinetics
At what rate does a chemical reaction occur?
Definition of Collision Theory (3)
- A reaction will most likely occur if
- Reactant Particles Collide
- With proper energy & orientation.
What are the 6 factors affecting the rate of a reaction?
- Nature of Reactants
- Concentration
- Surface Area
- Pressure
- Catalyst
- Temperature
How does the nature of reactants affect the rate of a reaction? (5)
- Breaking bonds require Activation Energy
- Slower reaction rate will occur
- Covalent Bonds break slower than Ionic Bonds
- Covalent shares e-, forming bonds
- Ionic bonds are from electrostatic attraction of opp. charges
How does concentration affect the rate of a reaction? (3)
- Higher Concentration = More Atoms
- More Atoms = More Collisions
- More Collisions = Faster Rxn
How does surface area affect the rate of a reaction? (4)
- Higher SA = More Exposed Areas
- More Exposed Areas = More Possible Areas for Collision
- More Possible Areas for Collision = More Collisions
- More collisions = Faster Rxn
How does pressure affect the rate of a reaction? (4)
- Only applies to gases
- Hi Pressure has same effect as Hi Concentration
- Gas particles are closer together, increasing collisions
- More Collisions = Faster Rxn
How do catalysts affect the rate of a reaction?
Catalysts provide an alternate pathway with a lower activation energy
How does temperature affect the rate of a reaction? (3)
- Temperature is the average kinetic energy of particle
- Faster Particles = More Collisions
- More Collisions = Faster Rxn
When is there a chemical change in compounds? (2)
- Compounds are formed or decomposed
- Reactant disappear and products appear
What happens to energy when bonds break and form? (3)
- When bonds break, energy is absorbed
- It takes energy to break bonds
- When bonds form, energy is released
Definition of Enthalpy (3)
- Amount of heat absorbed or released
- DURING A CHEMICAL CHANGE
- Measured in Joules
Δ H
How is Enthalpy Calculated?
ΔH = Enthalpy of the Product - Enthalpy of Reactant
Definition of Exothermic Reactions (5)
- Products have less E than reactants
- During a chemical rxn, extra E is released
- ΔH is negative
- Freezing & Condensation
- System is cooling down but surroundings are heating up
Definition of Endothermic Reactions (5)
- Reactants have more E than products
- During a chemical rxn, extra E is absorbed from surroundings
- ΔH is positive
- Melting & Boiling
- System is heating up but surroundings are cooling down
How do you read a PE Diagram? (6)
- Reactants are on the far left
- Products are on the far right
- Activation Complex is the peak
- Activation Energy (Forward Rxn) is vertical distance of peak & reactant
- Activation Energy (Reverse Rxn) is vertical distance of peak & product
- Enthalpy - Difference of Product & Reactant
- Dotted Lines Indicate a Catalyst
- Lowered Activation Energy
- PE of Product & Reactant stay the same
- ΔH is the same
What does Activation Energy ensure?
When molecules collide, they have enough energy for an effective collision
Definition of Equilibrium (5)
- Dynamic Process
- RATE of forward rxn = RATE of reverse rxn
- Can only occur in a closed system
- Concentrations are constant, not =
- No observable changes occur
Definition of Constant Concentration (3)
- Reactant & Product Concentration remain unchanged
- Once Equilibrium is Reached (= rates of forward & reverse rxn)
- Constant Activity but no Net - Change in Overall Amount
Definition of Closed System
Products & Reactants Cannot Leave or Enter the System
What are two types of equilibrium?
- Physical Equilibrium
- Chemical Equilibrium
What are two types of Physical Equilibrium (2)
- Phase Equilibrium
- Solution Equilibrium
Definition of Physical Equilibrium
Equilibrium is established during a physical change
Definition of Solution Equilibrium (5)
- Saturated Solutions are at Equillibrium
- Only occurs when more solute is added to a sat. solution
- No more solute can dissolve in a saturated solution
- So, some solute must recrystallize to allow it to dissolve
- Rate of dissolution = Rate of recrystallization
Definition of Phase Equilibrium (4)
- Equilibrium during a phase change
- Melting/Freezing & Evaporation/Condensation
- At 0°C, in a closed container, rate of freezing = rate of melting
- At 100°C in a closed container, rate of evaporation = rate of condensation
How can Solution Equilibrium shift? (3)
- Temperature/Pressure Changes (Stress)
- Rate of Dissolution > Rate of Recrystallization
- Continues until solution saturates at equillbrium
Definition of Chemical Equilibrium (2)
- Equilibrium at a Chemical Change
- Observable changes (color/pressure/temp.) will not occur
ex:
- Even though a rxn w/ a color change still occurs at a molecular level
- No color & macroscopic changes occur once equilibrium is established
- Bc of constant concentration of reactants & products
Definition of Le Châtelier’s Principle (3)
- A stress on a system at equilibrium
- Will change/shift the equilibrium
- To “relieve” stress
Definition of Stress (3)
- Any change in conditions on a system
- That affects the rate of a reaction
- Temperature, Concentration, Pressure, etc.
What is the effect of a concentration change to a system of equilibrium? (5)
- Increasing concentration of a substance
- Causes the reaction to shift
- To consume the substance
- To decrease the increased change of concentration
- To rebalance rxn at a new equilibrium
What is the effect of an increase in concentration of a reactant? (2)
- The reaction will shift to produce products
- In reversible rxns, the forward rxn will be favored
What is the effect of an increase in concentration of a product? (2)
- The reaction will shift to produce reactants
- In reversible rxns, the reverse rxn will be favored
What is the effect of an increase in temperature in a system of equilibrium? (3)
- The reaction will shift to favor the endothermic reaction
- BC it wants to absorb the extra heat that was added
- Consider heat as a product/reactant (you can use same logic as conc)
What is the effect of a decrease in temperature in a system of equilibrium? (3)
- The reaction will shift to favor the exothermic reaction
- There’s less heat to absorb, so endo rxn cannot perform at a faster rate
- Consider heat as a product/reactant (you can use same logic as conc)
What is the effect of a pressure increase in a system of equilibrium? (2)
- Only matters if there’s unequal moles of gases on both sides of rxn
- Reaction will shift to the side of rxn that produces fewer moles
What is the effect of a pressure decrease in a system of equilibrium? (2)
- Only matters if there’s unequal moles of gases on both sides of rxn
- Reaction will shift to the side of rxn that produces more moles
What is the effect of a concentration, temperature, & pressure change to Haber’s equation
N2 (g) + 3H2 (g) ⇌ 2NH3 (g) + heat
(3/2/2)
Concentration
1. Increasing Conc. of N2 or H2 will produce more NH3
2. Increasing Conc. of NH3 increases rate of decomposition, producing more N2 & H2
3. (When increasing H, N decreases bc N will be used at faster rate with lower conc.)
Temperature
1. Increasing temp. favors reverse rxn & production of N & H (endothermic)
2. Decreasing temp. favors forward rxn & production of NH3 (exothermic)
Pressure
1. Increasing pressure favors forward rxn & production of NH3 (fewer moles)
2. Decreasing pressure favors reverse rxn & production of N & H (more moles)
What is the effect of a catalyst on a system of equilibrium? (3)
- Does not shift equilibrium
- Increases rate of both forward & reverse rxn
- Also allows the system to reach equilibrium more quickly
