module 5 Flashcards
dynamic equilibrium
rates of forwards and reverse reaction are equal but non-zero
- concentrations are constant
eg. saturated solution of sodium chloride
what pracs can you use for reversibility
reversibility of the dehydration of cobalt (II) chloride
- hexahydrate pink
- anhydroussky blue
reversibility of combustion metals –> shows the lack of reversibility
- combustion of magnesium and steel wool
- no changes occur when placed in ice bath
system
boundary of where the reaction occurs and composed of both substances and energy
- open
- closed
closed system
- constant number of particles in a system (no matter transfer)
- energy can be exchanged with the surroundings
eg. sauce pan and lid
open system
- system can interact with the surroundings allowing for the exchange of matter and energy
eg. boiling water without a lid
static equilibrium
the rates of forward and reverse reaction are equal and zero
- irreversible reaction at completion eg. dissolution of salt in unsaturated solution
- irreversible reaction before initiation
eg. combustion of fuel without th initial spark
- reversible reaction with insurmountable activation energy
eg. diamond and graphite
modelling dynamic equilibrium
counters or cards
enthalpy
amount. of stored heat energy within a substance
H reaction = h products - h reactants
- reactants > products (exo) (more energy for bond forming) forward
- reactants < products (endo) ( more energy for bond breaking) reverse
- kJ mol-1
-J mol-1
combustion: negative enthalpy change
photosynthesis: positive enthalpy change
entropy
measure of state of disorder in a chemical system
- J mol-1K
kJ mol-1K
delta s = sum of s products - sum of s reactants
S<0 reverse
S>0 forward
combustion: positive entropy change
photosynthesis: negative entropy change
difference between enthalpy and entropy
absolute value and change
law of thermodynamics
- Zeroth Law of Thermodynamics
- if two systems are in thermal equilibrium with a third system, then they are in thermal equilibrium with each other - The First Law of Thermodynamics
- energy movement into or out of a system is in accordance with the law of conservation of energy - The Second Law of thermodynamics
- entropy of an isolated system not at equilibrium will increase over time, approaching maximum value at equilibrium - The Third Law of Thermodynamics
- the entropy of a system approaches a minimum as the temperature approaches zero
what is the enthalpy and entropy change in reverse reactions
H>0
collision theory
- based on the principle that all matter is made up of tiny particles which are in constant motion and reactant particles have successful or unsuccessful collisions
- collision theory explains that chemical reactions take place when molecules with sufficient energy collide at a correct orientation (successful collision)
- high conc (reactants) – collide at high frequency –> rate of reactants formed high –> conc of reactants decreases –> forward reaction reduces over time
- increased conc of products as they are being formed –> collision of reverse increases
- reaches dynamic equilibrium
- conc of both is rarely equal
how to increase rate of reaction through collision theory
- frequency of collisions increase
- individual collisions must have a higher chance of being successful
rate of reverse reaction is proportional to
products
rate of forward reaction is proportional to
reactants
Le Chateliers Principle
if a system is at dynamic equilibrium is disturbed, then the system will shift so to minimise the change until a new equilibrium is reached
- change in: volume/pressure, concentration, temperature
- the change will never be completely nullified
shift to the right
forward reaction begins to exceed rate of reverse reaction
shift to the left
reverse reaction begins to excess rate of forward reaction
concentration LCP
- increase reactants –> forward reaction –> right by LCP
- increase products –> forward reaction –> left by LCP
what has no effect if added or removed within a system on the equilibrium
liquids and solids (solvents accepted)
what happens if water is added to a system
concentration decreases –> favours forward reaction
endo or exo
reactants + heat –> products
endo
delta H > 0
endo or exo
reactantas –> products + heat
exo
delta H < 0