Equilibrium & energy Flashcards
ΔG is important for biology
- indicates if a process will or will not occur
- indicates how far from the equilibrium a process is
- indicates how much useful work may be available from the process
IfΔG < 0
IfΔG > 0
IfΔG = 0
IfΔG < 0 exergonic process
IfΔG > 0 endergonic process
IfΔG = 0 the system is at equilibrium
IfΔG is negative
the reaction is spontaneous, energy releasing (exergonic process)
IfΔG is positive
the reaction is non- spontaneous, with energy supplied (endergonic process – energy is absorbed)
GIBBS free energy change
ΔG =ΔH- TΔS
ΔG = free energy in the system ΔH = change in system’s heat content (enthalpy) ΔS = change in system’s entropy
The first & second thermodynamics are connected by_________
GIBBS free energy change
Natural process always move towards __________ disorder
During some process, the entropy in the system______________
increasing disorder
decreases, i.e. the system becomes more ordered, accompanied by work being done.
Unit for Entropy
ΔS , joules per degree (J/K or JK-1)
Absolute temperature is measured on
measured on the kelvin scale
273 K = 0C -273C =0 K
Third law of thermodynamic
only in the case of pure, crystalline substance at a temperature of absolute zero would the entropy be zero
Second law of thermodynamic
Since energy cannot be created or destroyed, it can only be re-arranged
First law of thermodynamic
Conservation states that energy is always conserved, it cannot be created or destroyed
Hee’s Law
the enthalpy change in the reaction doesn’t depend on the reaction pathway
ΔHx =ΔH1 +ΔH2
When writing thermochemical equation:
- Numbers of moles
- State of substance
- Specify temp the reaction is carried out at
ΔH
enthalpy change - the energy change per number of moles
Standard enthalpy of reaction
the energy change of a reaction
Standard enthalpy of combustion
the enthalpy change when 1 mole of substance is completely burned in excess oxygen under standard situation
Standard enthalpy of formation
the enthalpy change when 1 mole of compound is produced from its elements in standard conditions, all products and reactants in the standard state
Bond dissociation enthalpy (bond energy)
the energy needed to break one mole of chemical bonds
Change in enthalpy (enthalpy of reaction) formula
ΔH = H(products) – H(reactants)
Units for energy
joules or kilojoules (kJ)
Enthalpy
the energy associate with an element or compounds
System -
Isolated system –
Surrounding -
System - the objects been study
Isolated system – the objects which energy is impossible to transform to/ from
Surrounding - everything else in the universe
Thermochemistry
the study of the quantity of heat absorbed or evolved by chemical reactions
Thermodynamics
the science of the relationship between heat and other form of energy
Factors that affect reaction rate
Explain
~Concentration of reactants > effective collisions occur per unit time
~Temperature > speed up the movement of substance, increase chance of collisions
~ Presence of catalyst > A substance that can speed up the reaction, but chemically unchanged at the end of the reaction
~ Surface area > Increase chances of particles contact
~ Pressure (Gaseous reaction) – Increase the amount of particles in the same volume
In kinetic term, Ea is ?
the minimum amount of energy which colliding particles need in order to react with each other
ΔH
The difference between energy level of the reactants and products = the amount of energy taken in or given out during reaction
From the top of the curve to the products, going down the energy scale > ?
> Energy is given out as bonds are formed in products
Energy put in is less than energy given out > exothermic reaction
If the curve is going up the scale, energy is ________
At the top of the curve, bonds in the reactants are ______________
- energy is put in to break bond in the reactants.
- the bonds in the reactants have been broken.
ΔG
Free energy change
Activation Energy (Ea)
Minimum amount of energy required for the reaction to start
The amount of energy put in to breaks these bonds
Endothermic –
Exothermic –
Endothermic – energy taken in for reaction
Exothermic – reaction release energy
_______ energy need to break strong bond; _______ energy need to break weak bond
More energy need to break strong bond; less energy need to break weak bond
Energy is stored in________
intramolecular bond (covalent/ ionic/ metallic)
Bonds can be __________ during chemical reactions
Energy is _________to break bond
- rearranged
- required
Why need energy?
- Mechanical work e.g. muscle contraction
- Generate light & electricity
- Active transport, neurotransmitter
- Synthesis complex biomolecules using simple precursors
Kinetic
a movement of waves, electrons, atoms, molecules, substances, and objects
Potential (Stored)
E.g. Chemical energy is the energy stored in the bonds of atoms & molecules
What don’t appear in a heterogenous equilibrium constants
~ Solid concentration can’t change because it’s molecular weight and density are constant
~ Pure liquid concentration doesn’t vary, they don’t appear in the equilibrium expressions
heterogenous equilibrium constants formula
Kc = [C][D] / [A][B]2
Equilibrium constant formula in a homogenous system
Kc = [C]^c[D]^d / [A]^a[B]^b
Kc = equilibrium of concentration
[ ] = concentration in mol/dm3
a = Number of substance
Right hand side of equation on top / left hand at the bottom
What gives the equilibrium constant?
Measure concentration of everything when a reaction reaches the equilibrium
Equilibrium constant allows us to ________
to make qualitative judgment about the reaction, if the mixture is mostly products or mostly reactants
Le Chatelier’s Principle for changes in pressure
- Changes in Volume of Gaseous Equilibrium Systems
- Gas volume is related to gas pressure - a gas at reduced volume has a higher pressure (more chance of collisions)
- A gas at increased volume has a lower pressure
How to set up the dynamic equilibrium
the rates of the forward reaction and the back reaction have to become equal.
This doesn’t happen instantly. For a very slow reaction, it could take years!
A catalyst speeds up the rate at which a reaction reaches dynamic equilibrium.
Le Chatelier’s Principle
If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change
Eg. changing concentration, pressure (for gaseous reactions) or temperature, or adding more molecules.
Heterogenous equilibria
Products/reactants in more than one phase
Homogenous equilibria
everything in the equilibrium mixture is present in the same phase
Dynamic equilibrium
the forward/ reverse reaction is continuing and the rate of both reactions are equal
Chemical equilibrium
Reaction can go forward or reversed, occurring at the same rate without net change in energy
The tendency for a reaction to reach a equilibrium is driven by
the Gibbs free energy (ΔG )
K(eq)
equilibrium constant
K(eq)= [C][D] / [A][B]
Formula of relationship between GIBBS free energy change and equilibrium constant
ΔG ^0 = -RT. In.K(eq)
Redox reaction
transfer of e -
Reduction - gain e-
Oxidation - lose e-
Chemical that oxidised is the ______ agent
Chemical that reduced is the _______ agent
oxidised, reducing agent
rreduced, oxidising agent
redox potential
A measure of the tendency for a species to gain or lose electrons
Redox potentials are measured in
volts (E°)
negative value of (E°) tend to ______
Positive value of (E°) tend to ______
negative value of (E°) tend to oxidise
Positive value of (E°) tend to reduce
Oxidation number
losing e- , increasing in oxidation number
gaining e- , decreasing in oxidation number
How to calculate the bond energy
- Balance equation
- Draw the structure
- Count the bonds and add up bond energy on both side
- Calculate ΔH = energy of bond broken - energy of bond formed (kJ/mole)
Bond energy (bond dissociation energy)
energy required to break bond
a measure of chemical bond strength
Alternative way to find out enthalpy change
Breaking bond _______ energy
Forming bond ________ energy
Breaking bond need energy
Forming bond release energy
Rules of thermochemical equation
- enthalpy is directly proportional to mass
- ΔH for a reaction is equal in magnitude but opposite in sign to ΔH for the reverse reaction
- It is independent of the number of chemical steps involved (Hee’s Law)
Rules for redox reaction
- Half the equation
- understand the e- transfer directions
- Balance the charges
- Put 2 side back together
