Studied by 1 person
Nitrogen as an element exists as…
A diatomic gas
How many bonds can N form?
Three bonds
Reactivity of nitrogen (and explain why)
It is very unreactive because of the v.strong triple bond which needs a lot of E to break
Name the 3 main nitrogen compounds
NO / NO2 / N2O
Why do plants need nitrogen?
For growth
Predict the appearance (/state) of NO2 at RTP
A brown gas
Source of NO
Car engines
Source of N2O
From bacteria in the soil
State the conditions of dynamic equilibrium (3)
Rate forward is equal to the rate backwards / conc of R and P are constant / closed system
How to find the rate on a conc vs time graph
Find the gradient
Describe the POE when Kc = 1
POE is in the middle
Describe the POE when Kc > 1
POE is towards products
Describe the POE when Kc < 1
POE is towards reactants
Kc ONLY changes with…
Temperature
What does ICEE represent? (Each letter)
Initial mol / Change in mol / Equilibrium mol / Equilibrium conc
What is Chatelier’s principle?
If a system at equilibrium is disturbed the POE shift to oppose the change
State the 2 main ways of removing a chemical from an equilibrium reaction?
Physically / chemically
Describe the effects of changing (increase) pressure on the POE
Increasing pressure, POE shifts to the side with least moles of gas
3 points in finding Kc by experiment
Mix known amounts of reactant / wait for equilibrium to be reached / do an experiment (titration) to find the conc of one chemical in the mixture
Define rate
Change in [R or P] / time
Define activation energy
The minimum combined E needed for a reaction to occur when 2 particles collide
What is an intermediate?
A chemical made in one step but used in another
A chemical used in one step and remade in another is…
A catalyst
What is the slowest step called?
The rate determining step (rds)
What does the overall rate of a reaction depend on?
The slowest step (rds)
What can affect the overall rate of reaction?
Chemicals IN OR BEFORE the rds
What is the (1) main property of the ‘slowest’ step
It has the highest Ea (activation energy)
What is molecularity?
It tells us how many particles are in the rds.
If [R]1 in the rate expression
Only 1 lot of that chemical is involved in or before the rds / reaction is 1st order wrt R / double the [R] = double the rate
If [R]2 in the rate expression
2 lots of that chemical is involved in or before the rds / reaction is 2nd order wrt R / double the [R] = quadruple the rate
If the R is not include in the rate expression
Chemical is not involved in or before the rds / reaction is 0 order wrt R / double the [R] = no change in the rate
What is the overall order?
All the orders in a rate expression added up.
Mechanism for 1st order means:
1 lot of that chemical in or before the rds
Mechanism for 2nd order means:
2 lots of that chemical in or before the rds
Mechanism for 0 order means:
0 lot of that chemical in or before the rds / only used after the rds
Why is a reaction with 3 reactants, statistically unlikely?
The 3 particles would have to collide simultaneously, which is highly unlikely.
Describe the appearance of a conc vs rate graph for 0 order
A straight horizontal line
What happens to macroscopic properties in dynamic equilibrium?
A system at dynamic equilibrium has no change in macroscopic properties
(T/F) The position of equilibrium can only ever be exactly in the middle of the reactants and the products
False
What is K ?
Kelvin
What is k
Rate constant
State how the rate constant, k varies with temperature T?
As temperature increases k increases exponentially
How to find Ea? (3 steps)
Find gradient / x 8.314 / divide by 1000
Units for Ea
KJmol-1
What would be the units for 1/T?
K-1
Relationship between rate and k
Rate is proportional to k
What can you use instead of Ln(k)? (2 options)
Ln(rate) / Ln(1/time)
How many trials should you do (in an experiment) and why?
5 trials, need 5 points to plot a graph
Why should you not use trial 5?
Because trial 5 is too quick
Explain why 2NO2 + F2 → 2NO2F may not agree to the mechanism?
3 particles would have to collide simultaneously, which is highly unlikely (/statistically unlikely)
State what is happening to the forward and reverse reactions once equilibrium has been reached?
Rates are equals
Suggest why industrial process might not use high pressures?
High pressure is too expensive
Suggest why industrial process might not use low temperatures?
Low temperature makes the process slow / reaction rate low
Suggest why is it unlikely that carbon dioxide stored under the ocean would escape back into the atmosphere?
High pressure under the ocean keeps the CO2 in place
Give one polluting effect of carbon monoxide?
Its toxic
Give one polluting effect of carbon dioxide?
It causes global warming / greenhouse effect
Give 2 ways that can remove CO2 from the atmosphere?
Plant more trees / promote photosynthesis by phytoplankton
limfaow
limfaow
How can half life show if a rxn is first order?
Half life is constant
Units for rate constant from 1st order reaction
s-1
What is the Arrhenius equation used for?
To calculate a value for the activation energy Ea
When can colorimetry be used?
When only 1 substance is coloured
Relation between absorbance and concentration
Absorbance is proportional to concentration
2 main things to do before using a colorimeter
Zero it with water / choose filter with complementary colour
What does a calibration curve graph show?
Absorbance vs time
In what circumstance, is volume NOT needed when calculating Kc
When sum of the coefficients on the left = sum of the coefficients on the right
On the Y axis of an Arrhenius graph, u should plot
Ln(k)
What (2) measurements can we take for reactions with gas products, to find rate?
Volume of gas made / Mass loss if a gas is made
What (2) gases cannot be measured for ‘mass lost if gas is made’ and why?
Hydrogen gas bc its too small & light / toxic gases bc its toxic
What (2) measurements can we take for reactions with ionic R / P, to find rate?
Conductivity if many ions / pH for [H+]
Whats the fancy word for samples
Aliquot
How does increasing conc/pressure affect rate?
It increases rate by increasing the frequency of collisions
How does increasing surface area affect rate?
It increases rate by increasing the frequency of collisions
How does increasing temperature affect rate?
It increases rates by increasing the frquency of collisions AND proportion of collisions with E>Ea)
How does a catalyst affect the rate of a reaction?
It increases rate by increasing proportion of collisions with E>Ea
Suggest one way to increase surface area of a solid reactant
Use it in powder form
Suggest 2 ways of collecting a gas made from a reaction
Gas syringe / through water
What are the 3 gases that you cannot collect through water?
Steam / HX / CO2
What chemical is made when CO2 is dissolved in water?
Carbonic acid
How would you calc average rate? (the equation)
Total amount made / total time taken
What is the typical units for rate?
moldm-3s-1
What are the units of the rate constant for a reaction that is third order overall? (mol first)
mol-2dm6s-1
Can the rds involve a catalyst?
Yes
What 2 main things cannot be in the rate expression?
An intermediate / A chemical that is 0 order
How many half-lives must you construct on a graph?
At least two half-lives
What are the units of the rate constant for a reaction that is first order overall?
s-1
What happens when hydrogen halides mix with water
Make acidic solutions
Solubility of hydrogen halides
Very soluble
What type of bonds to hydrogen halides have?
Covalent bonds
Test for HX (include observation)
React with NH3 to make NH4+X- (s) which produce steamy white fumes
Product of the reaction HX(g) + NH3 (g). (include state symbols)
NH4+X- (s)
Rewrite the equation on making hydrogen halides (include state symbols)
NaX (s) + c.H2SO4 (aq) —> NaHSO4 (aq) + HX (g)
What observation would you see in the reaction: NaX (s) + c.H2SO4 (aq) —> NaHSO4 (aq) + HX (g)
White fumes
In what ways can you collect hydrogen halides?
Through gas syringe (only)
What are the products for HBr + H2SO4 ? (include state symbols)
Br2 (g) + SO2 (g) + H2O (l)
What are the observations for the reaction HBr + H2SO4?
Orange gas
What are the products for HI + H2SO4 ? (include state symbols)
I2 (g) + H2S (g) + H2O (l)
What are the observations for the reaction HI + H2SO4?
Purple gas / rotten egg smell
What chemical has a rotten egg smell?
H2S (g)
Source of NO2 ?
Car engines / oxidation of NO
Note 
Flashcard (201)