Equilibria, Energetics and Elements P 2

In a rate-concentration graph there is a single horizontal flat line, determine the order of the compound
Zero-order with respect to compound
What is the formula for the rate equation?
Rate=k[A]^[B]^
In a two step mechanism what is the name of the first step?
The rate determining step
What are the reactants in the rate determining step?
The compounds found in the rate equation
Produce a two-step mechanism for this:

H2 + 2ICl -> 2HCl + I2

rate=k[H2][ICl]

H2 + ICl -> HCl + HI
HI + ICl -> HCl + I2
Define the term lattice enthalpy
The enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions
State the meaning of the term ligand
Donates an electron to a metal ion / forms a coordinate bond to a metal ion
What is the difference between a strong acid and a weak acid?
A strong acid completely dissociates and a weak acid partially dissociates
Explain what is meant by the term Bronsted-Lowry base
Proton acceptor
Why is it difficult to predict if the lattice enthalpy of magnesium sulfide would be less/more exothermic than that of sodium oxide?
Mg2+ is smaller and Mg2+ has a greater charge
S2- is larger
But Mg2+ has stronger attraction and S2- has weaker attraction
What is a property of cobalt(II) and cobalt(III) that is typical of transition ions?
They are catalysts or coloured
CoSO4(aq) reacts with NaOH(aq) what is the transition element species formed? And what type of reaction is it?
Co(OH)2
Precipitation
CoSO4(aq) reacts with HCl(aq) what is the transition element species formed? And what type of reaction is it?
CoCl4^2-
Ligand substitution
Write an expression for Ka of HNO2
Ka=([H+][NO2-])/[HNO2]
Ca(OH)2(aq) + HNO2(aq) write the overall equation and ionic equation
Ca(OH)2 + 2HNO2 -> Ca(NO2)2 + 2H2O
H+ + OH- -> H2O
How does equilibrium allow a buffer to control pH?
Added alkali reacts with H+
Shifting equilibrium to produce more H+

Added acid reacts with conjugate base(salt)
Equilibrium shifts towards HA

What is needed for testing cell potentials?
Voltmeter
Salt bridge
Electrode (Pt or metal)
1 mol dm^-3 concentration
What are the three ways being developed to store hydrogen for fuel?
Absorption in a solution
Adsorption on a solid
Liquid under high pressure
Write the equation that links free energy change with enthalpy change and temperature?
/G=/H – T/S
Why could an exothermic reaction occur at low temperatures but not at high temperatures?
T/S is more negative as temperature increases
At high temperature T/S is more negative than /H
When is a reaction feasible?
/G<0 or /G=0
What is the formula for Kc?
[concentration of product]^mol / [concentration of reactant]^mol
What does pressure, temperature and concentrations do to Kc?
Pressure and concentrations do not affect Kc
Only temperature affects Kc
The system increase/decreases products and reactants to maintain Kc
Define lattice enthalpy
Formation of one mole of an ionic conditions from its gaseous ions under standard conditions
Why do ionic compounds differ in melting points?
There is greater attraction from smaller ions
More (heat) energy to overcome attraction
What happens when there is a decrease in entropy?
There is less disorder
If enthalpy and entropy are both negative how will feasibility change as temperature increases?
Reaction becomes less feasible
/G increases
T/S becomes more negative
How can you work out entropy?
Entropy of products – entropy of reactants
What is the equation for /G?
/G=/H-T/S
When does a reaction become feasible?
/G=0
Write an expression of Kc for 2CH4->C2H2 + 3H2
[C2H2][H2]^3/[CH4]^2
What happens to the initial rate when temperature is increased?
Initial rate increases
What happens to the initial rate when pressure is increased?
Initial rate increases
What happens to the initial rate a catalyst is added?
Initial rate increases
Give two examples of large-scale uses of hydrogen
Fuel cells
Manufacture of margarine
Making ammonia
Making HCl
Making methanol
Why would a reaction take place in multiple steps?
Stoichiometry in rate equation does not match stoichiometry in overall equation
Collision unlikely with more than 2 ions
Draw a rate concentration graph of something that is first order
[image]
Draw a rate concentration graph of something that is second order
[image]
How do convert pKa to Ka?
10^-pKa
What are the two general equation for Ka of a weak acid?
Ka= ([H+][A-])/[HA] OR [H+]^2/[HA]
What is the equation for pH?
pH=-log(H+)
Why are Sc and Zn not transition elements?
A transition element has an ion with an incomplete d-orbital
Sc and Zn are not transition element
Sc3+ is 1s2 2s2 2p6 3s2 3p6
Zn2+ is 1s2 2s2 2p6 3s2 3p6 3d10
Sc3+ d-orbital is empty
Zn2+ d-orbital is full
How does H2NCH2CH2NH2 act as a bidentate ligand?
Electron lone pair of N
Donates two electron lone pairs to a metal ion
What would make a compound have stronger ionic bonds?
Greater ionic charge
Smaller ionic size
What does a y=x rate-concentration graph show?
1st order with respect
What is the formula for rate equation and what is k?
rate=k[]^order
k is the rate constant
How can weak acid be proved by a single pH test?
Measured pH is > 0
What is the acid dissociation constant?
Ka
What is the formula for Ka of a weak acid?
Ka=([H+]?/[HA])
What is the relation between the concentration of H+ and pH?
[H+]=10^-pH
What is the equation for Kw?
Kw=[H+][OH-]
What is a buffer formed from?
A weak acid and a salt of the weak acid
What happens when acid is added to a buffer?
Conjugate base reacts with added acid
Equilibrium shifts to restore conjugate base (usually left)
What happens when alkali is added to a buffer?
Weak acid reacts with added alkali
Equilibrium shifts to restore acid (usually right)
What is needed to set up an electrochemical cell?
Voltmeter
Salt bridge
Electrodes
1 mol dm-3 solutions in each
What reaction is on the right hand side of the electrochemical cell?
Reduction
How is cell potential worked out?
E(positive terminal (left))-E(negative terminal (right))
What carries the charge through the wire of an electrochemical cell?
e-
What carries the charge through the solution of an electrochemical cell?
ions
What is the main difference between an electrochemical cell and a fuel cell?
A fuel cell converts energy from the reaction of a fuel with oxygen into a voltage
What is the overall reaction in a fuel cell?
2H2 + O2 -> 2H2O
What are the ways to store hydrogen?
Under pressure as a liquid
Adsorbed on solid
Absorbed within solid
Why is the use of hydrogen for fuel considered the same as fossil fuels?
Energy is needed to make the hydrogen
What is the expression for Kc?
Kc=([products]^mol/[reactant]^mol[reactant]^mol)
What side does equilibrium favour when pressure is increased?
The side with the least moles
When pressure increases what happens to Kc?
Kc does not change
Increase in pressure causes the system to no longer be in equilibrium
So top of Kc expression increases and bottom decreases until Kc is reached
What is another method other than using fossil fuels to produce hydrogen?
Electrolysis of water
What is needed for a reaction to be feasible?
/G < 0
What is the expression for /G?
/G = /H – T/S
What is the expression for /S?
/S = (sum of products) – (sum of reactants)
If T/S is negative why would an increase in temperature cause a reaction to not be feasible?
As temperature increases T/S becomes more negative
Eventually /G becomes positive
What are the two transitional metals with a partially filled 4s sub-shell?
Chromium and copper
What electrons get lost first in transitional metals?
4s electrons
What is a ligand?
A molecule that donates an electron pair to a metal ion to form a coordinate bond
How can a molecule act as a bidente ligand?
Lone pairs on two atoms
Donates two electron pairs
Forms two coordinate bonds
What are the three ways to follow the rate of reaction?
Record gas volume
Observe colour changes
Electrical conductivity changes
What is the reaction rate?
Change in amount of compounds per unit time
What is the half life?
The time its takes for half of the reactant to be used up
What has a constant half life?
First order reaction
What is a clock reaction?
A reaction where you can easily measure the time before a product is formed
What affects the rate constant (k)?
Temperature
A higher temperature does what to the rate constant (k)?
Increases it
How is equilibrium formed?
As reactants get used up forward reaction slows down
As more product is formed the reverse reaction speeds up
Till the rate of the forward reaction is the same as the reverse reaction
What are the two main things needed for dynamic equilibrium?
A closed system
A constant temperature
What is the only thing that affects Kc?
Temperature
Why does temperature affect Kc?
Change means more product is formed
Kc will increase
What do cells use as a buffer solution?
H2PO4- <-> H+ + HPO4^2-
Dihydrogen phosphate ions and Hydrogen phosphate ions
What does the blood use as a buffer solution?
H2CO3 <-> H+ + HCO3-
Carbonic acid
Whats a strong acid/strong alkali titration graph look like?
[image]
Whats a strong acid/weak alkali titration graph look like?
[image]
Whats a weak acid/strong alkali titration graph look like?
[image]
Whats a weak acid/weak alkali titration graph look like?
[image]
The horizontal line of a titration curve indicates?
Equivalence point
Neutralised
What is methyl oranges pH of colour change? and what is the colour change?
Red to Yellow
3.1-4.4
What is phenolphthalein pH of colour change? and what is the colour change?
Colourless to pink
8.3-10
What are the properties of transition metals?
Form complex ions
Variable oxidation states
Coloured compounds
Good catalysts
What is the colour change that accompanies
Cu2+ + 2OH- -> Cu(OH)2
Pale blue to blue precipitate
What is the colour change that accompanies
Co2+ + 2OH- -> Co(OH)2
Pink to blue precipitate that goes back to pink
What is the colour change that accompanies
Fe2+ + 2OH- -> Fe(OH)2
Pale green to dark green precipitate
What is the colour change that accompanies
Fe3+ + 3OH- -> Fe(OH)3
Yellow to dark orange/brown precipitate
What is a transition element?
Forms a stable ion with an incomplete d sub shell
What is a complex ion?
A transition metal coordinately bonded to one or more ligands
What is a coordinate bond?
Dative covalent bond where a shared pair of electrons come from the same atom
What is a ligand?
A molecule that can donate a pair of electrons to form a coordinate bond
What do you call a ligand with two lone pairs?
Bidentate
What is the structure for platin?
NiCl2(NH3)2
How is cis-platin used to treat cancer?
Binds to DNA of cancer cell
Prevents reproduction
What is the reaction and colour change of aqueous copper(II) ions and ammonia?
[Cu(H2O)6]2+ + 4NH3 <-> [Cu(NH3)4(H2O)2]2+ + 4H2O

Pale blue to deep blue

What is the reaction and colour change of aqueous copper(II) ions and chloride?
[Cu(H2O)6]2+ + 4Cl- <-> [CuCl4]2- + 6H2O

Pale blue to yellow

What is the reaction and colour change of aqueous cobalt(II) ions and chloride?
[Co(H2O)6]2+ + 4Cl- <-> [CoCl4]2- + 6H2O

Pink to blue

What is the reaction and colour change of aqueous cobalt(II) ions and ammonia?
[Co(H2O)6]2+ + 6NH3 <-> [Co(NH3)6]2+ + 6H2O

Pink to brown

What does a larger Kstab mean?
Ion is very stable
What is meant by stability constant?
Equilibrium constant for the formation of a complex ions from it constituent ions
Draw the structure of haemoglobin
[image]
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