CHEMICAL INDUSTRY

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

(Evaluate) 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

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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)

Write 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