unit 9 - kinetics & equilibrium Flashcards
a chemical equation describes
a chemical change (reaction)
kinetics
deals with the rates of chemical reactions
rate
describe how fast a reaction takes place
high rate
= fast (less time)
low rate
= slow (more time)
collision theory
For reactions to occur reactant particles must collide.
1) Spatial Orientation must be exact
2) Activation Energy must be met
more effective collisions: temperature
Increase in temperature increases reaction rates, due to more KE.
more effective collisions: concentration
The greater the concentration (M) of reactants, the greater the reaction rates.
more effective collisions: nature of the reactants
Ionic substances react faster (dissociate) than covalent ones
(larger & contain more bonds).
more effective collisions: surface area
Increase in surface area, increases the reaction rate because more
surfaces are exposed.
**powder
more effective collisions: pressure
Increase in pressure on gases
increases reaction rates, because it
increases the concentration of the
particles.
**Little or no effect on solids & liquids
more effective collisions: catalyst present
Increase the reaction rate by providing lowering the activation
energy & creates an alternate pathway.
potential energy
is the energy stored within the bonds of reactants and products of a reaction.
Heat Content (Heat of Reaction)
amount of heat absorbed or released in a chemical reaction
Heat of Reaction (ΔH = PEproducts – PEreactants)
PED - Endothermic Reactions
- Gain more energy than is released
- Energy of the products is higher
than the reactants - Energy is absorbed
● ΔH is + (positive)
PED - Exothermic Reactions
- More energy is lost to the surroundings
- Products have less energy than
the reactants - Energy was released
- ΔH is - (negative)
∆H is the…
difference between the energy
needed to break the bonds in the reactants, and the energy given out when new bonds are formed in the products
ΔH is positive when the reaction is endothermic.
Heat of products are greater than reactants
ΔH is negative when the reaction is exothermic.
Heat of reactants are greater than the products
Endothermic: heat is a…
reactant (on left side)
Ex. N2 + O2 + 182.6 KJ → 2NO
Exothermic: heat is a…
product (on right side)
Ex. 2H2 +O2 → 2H2O + 486 KJ
(Δ H) is defined as the
difference in PE of the Products and the PE of the reactants
aka heat of reaction
Δ H is proportional To the AMOUNT of Material undergoing reaction.
Heat of Reaction & Surrounding Temperature: Exo Rxn
-Release Energy so the surrounding temperature (outside the reaction) gets warmed.
Ex. Heat Pack
Ex. From Table I the dissolving of NaOH (s), LiBr (s)
Heat of Reaction & Surrounding Temperature: Endo Rxn
-Absorb Energy so the surrounding temperature (outside the reaction) gets colder
Ex. A Cold Pack
Ex: From Table I the dissolving of KNO3, NH3Cl, NH4NO3
Surface Temp: Exothermic
Reactions in which Heat is Released to the surroundings
- Contents of test tube get Hotter
-Surrounding Temperature INCREASES
Surface Temp: Endothermic
Reactions where Heat is Absorbed from the surroundings
- Contents of test tube get Colder
- Surrounding Temperature DECREASES
equilibrium
is the state of balance between 2 opposite reactions occuring at the same time
- most reactions are reversible -><- must take place in a closed system
the state of equilibrium is…
dynamic = changing
equilibrium is reached when the reaction rates:
(Forward →) & (← Reverse) ARE EQUAL (are the same)
AT EQUILIBRIUM, concentration of reactants
≠ concentration of products
- concentration of reactants and products are CONSTANT (staying the same)
point of equilibrium (balance) is affected by:
- Temperature Change (Δ T)
- Change in [ ] Concentration
- Change in Pressure (on gases)
reaction non-reversible
goes to completion
A Reaction is NON - REVERSABLE when:
- a product is removed
- a product is a gas & the gas escapes
ex: NaHCO3 + HCl → NaCl + H2O + CO2 (g) - a product is a precipitate (insoluble) and can not react again **double replacement, table F
- a product is H2O
types of physical equilibrium: phase equilibrium
Ex. H2O (s) → H2O (l) If no Δ T
←
- At 0°C in a closed container, both water and ice exist at the same time.
** remember: melting point = freezing point
Ex. H2O (l) → H2O (g) If no Δ T
←
- At 100°C in a closed container, both liquid and gas exist at the same time.
phase equilibrium: in the open container
liquid evaporates until it is completely evaporated
H2O (l) -> H2O (g)
in the closed container
evaporation continues but it is balanced by condensation
H2O ( l ) → H2O (g)
←
types of physical equilibrium: solution equilibrium
dissolving
NaCl (s) → NaCl (aq)
←
recrystallization
- rate dissolving = rate recrystall.
- solution is saturated
Solubility
Mass of solute (solid) which can
dissolve in a given amount of solvent.
equilibrium is reached when the
concentration of the reactants and products remain constant
- the rate of the forward reaction equals the rate of the reverse reaction so there is no net change in the system
Le Chatelier’s Principle
if a chemical system at equilibrium is disturbed it will change (SHIFT) in the direction to relieve the stress
- the result is a new equilibrium at a diff point
how is stress applied
- change of concentration of reactants or products
- change of temperature
- change of pressure
equilibrium: increase in concentration
- if concentration of a substance increases, the reaction that reduces the substance is favored
equilibrium: increase in temperature
- temperature increase will shift a system in equilibrium to favor the endothermic reaction (to use up heat)
equilibrium: decrease in concentration
if concentration of a substance decreases, the reaction that increases that substance is favored
equilibrium: decrease in temperature
temperature decrease will shift a system in equilibrium to favor the exothermic reaction (replace the heat lost)
le chatelier’s principle: PRESSURE
- pressure only effects the equilibrium of a system in which GASES are involved
- pressure does not effect the equilibrium when there is no change in moles of gas
equilibrium: increase in pressure
an increase in pressure will favor the direction with fewer moles of gas
equilibrium: decrease in pressure
a decrease in pressure favors the direction with more moles of gas
le chatelier’s principle: catalysts
- catalyst increase the rate of both the forward and reverse reactions equally
- equilibrium is not disrupted and the concentration of reactants and products stay constant
common ion effect
ex: NaOH (s) ⟷ Na+ (aq) + OH- (aq) + 10.6 kcal
- add KOH (adds OH-), amt NaOH (s) increases, Na+ decreases
entropy
a degree of randomness or disorder
More Organized → More Disorder
Solid to Liquid State
Solid to Gas State
Liquid to Gas State
NI3 (g) → N2 (g) + 3 I2 (g)
NaCl (s) → NaCl (aq)
Spontaneous Reactions:
A reaction that when initiated will continue without any outside influence.
Spontaneous Reactions are more favorable when:
1) Reactions are Exothermic- lower activation energy & Loss of energy (more stable state)
2) Increase in Entropy- Increase in Disorder
In nature systems usually move in the
exothermic and more disorder direction
what does nature prefer
- analogy: bedroom
- low energy and high entropy
Law of Mass Action:
When a reversible reaction reaches equilibrium there is a mathematical relationship between the reactants and products.
what can Law Of Mass Action help predict
This can help us predict if the product or reactant concentrations would be greater at equilibrium or if they will be equal.
what is included in Keq equations
**Only concentration of gases and ions are included in the expression, OMIT solids & liquids.
what is Keq used to predict
Keq value is used to predict the concentration of products and
reactants at equilibrium
Keq greater than 1
→ there are more products than
reactants at equilibrium
Keq less than 1
there are more reactants than products
at equilibrium
Keq = 1
[Products] = [ Reactants] at equilibrium
when there is a decrease in volume, the equilibrium will shift to favor the
direction that produces fewer moles of gas
when there is an increase in volume, the equilibrium will shift to favor the
direction that produces more moles of gas
