The Chemical Industry Flashcards
What is the structure of N2? Where are the lone pairs?
It is N≡N. It is two nitrogens that have a triple bond.
Each nitrogen has a lone pair
What is the bond enthalpy of N≡N? What does this mean for the activation enthalpies for reactions involving N2?
It is very large 945kJmol-1
The activation enthalpy is therefore very high
What is the reaction to form ammonia?
N2 + 3H2 ==> 2NH3
What is the structure of NH3?
It has 3 hydrogen-nitrogen bonds and one lone pair.
How is NH4+ formed?
The lone pair on the nitrogen attracts a H+ ion and this forms a NH4+ ammonium ion
What type of bond is formed when NH3 reacts with H+?
The bond that is formed is a dative covalent bond. The nitrogen donates two electrons
What is the appearance and where does it come from for:
a) nitrogen oxide (NO)
b) nitrogen dioxide (NO2)
c) dinitrogen oxide (N2O)
a) NO is a colourless gas that turns into NO2 when in air. It comes from combustion in vehicles, thunderstorms and from denitrifying bacteria
b) NO2 is a brown gas and forms from the oxidation of NO
c) N2O is a colourless gas that is formed in the soil by denitrifying bacteria
What is the equation for the creation of nitrogen oxide?
N2 + O2 ==> 2NO
What is the shape and bonding of nitrate(III)? How common is it?
Two oxygens bonded to a nitrogen(III) a single bond and then both of the oxygens share a delocalised bond to the nitrogen. The nitrogen has a lone pair.
It is not very common.
What is the shape and bonding of Nitrate(V)? How common is it?
It is made from a nitrogen(V) with 3 oxygens joined by a single bond. and then all the oxygens are joined to the nitrogen by another delocalised bond.
Are NO3- and NO2- soluble in water?
They are very soluble
How are NO2- made from NH4+? What is the name of the process?
NH4+ + 1.5O2 ==> NO2- + 2H+ + H2O
The process is called nitrification
How is NO3- made? What is the name of this process?
NO2- + 0.5O2 ==> NO3-
This is oxidation
How can you test for nitrate ions?
You react the nitrate ions with sodium hydroxide with Devardas alloy and an aluminium complex and ammonia is produced and this can be tested with litmus paper and turn it blue.
3NO3- + 8Al + 5OH- + 18H2O ==> 3NH3 + 8[Al(OH)4]-
What is Devardas alloy?
It is an alloy of Cu, Al and Zn
What is another test for ammonia?
When it comes into contact with hydrogen chloride gas it forms a white smoke
How can ammonium ions (NH4+) be tested for?
When reacted with sodium hydroxide it will produce ammonia which can be tested.
NH4+ + OH- ==> NH3 + H2O
What is the equilibrium constant? What is the symbol?
This is the measure of the position of equilibirum
Sumbol: Kc
What is the equation for the equilibrium constant for the reaction aA + bB <=> cC + dD?
Kc = [C]^c [D]^d / [A]^a [B]^b
Products / reactants
How much does the equilibrium constant vary?
Greatly
How does increasing the pressure change the position of equilibrium?
It moves the position of equilibrium to the side with the fewer gas molecules. This is because the reaction want to reduce the pressure.
What is Le Chateliers principle with regards to the position of equilibrium?
The position of equilibrium changes as to counteract the change in pressure as much as possible so that the magnitude of Kc can stay constant.
What happens to the position of equilibrium when the pressure is increased for the reaction of:
CH4 + H2O <=> CO + 3H2
It moves to the left because there are fewer gas molecules
What happens to the position of equilibrium when pressure is increased for the reaction of:
CO + 2H2 <=> CH3OH
It moves to the right because there are 3 gas molecules on the left and 1 on the right
Is the value of Kc affected by a change in pressure or concentration? (comparing before and after)
No, because the reactions counters the change keeping Kc constant
Does temperature affect the value of Kc?
Yes
For an increase in temperature, which direction is favoured for an endothermic reaction?
The products
For an increase in temperature, which direction is favoured for an exothermic reaction?
The reactants
How does a catalyst affect the position of equilibrium?
It has no effect
What are some examples of how to measure the position of equilibrium?
pH measurements
Colorimetric methods
Titrations
What is the rate of a reaction?
This is the rate at which the reactants form products
What is the key way factor that changes during a reaction as it progresses?
The concentrations of the products and the reactants
What is the rate of formation of products when compared with the rate of consummation of reactants?
The same
What is the equation to determine the rate of a reactions?
Rate = Change in property / time
What properties of a reaction can be measured to determine the rate? Which interfere with the reaction? (5)
Volumes of gases evolved Measuring mass change pH measurements Colorimetry Chemical analysis*
- interferes with the reaction
How can the volume of gas evolved be measured?
Using an upturned cylinder or gas syringe
How can the mass change be measured?
By placing the reaction on a balance
How can colorimetry be used to measure the rate of a reaction?
The colour can be measured through out the reaction and plotted on a graph
How is chemical analysis used to measure the rate of a reaction? What is this process called?
Samples are taken from the reaction and then the reaction has to be stopped before being analysed. This process is called quenching.
What is an example of chemical analysis?
Titrations with iodine thiosulfate or an acid-base titration
How can the rate of the decomposition of hydrogen peroxide be calculated?
By collecting the oxygen gas produced using an upturned cylinder of gas syringe and measuring the volume at different time intervals. A graph can then be drawn of volume of O2 against time. The gradient is the rate
Describe what is often seen on a graph volume of O2 against time. What is its shape?
The graph starts steep and the rate of the reaction starts fast. The reaction is fastest when the concentration of hydrogen peroxide is high.
The graph gradually flattens out when the hydrogen peroxide is used up and the reaction slows down and when it is flat the reaction has come to a stop.
What is the rate of a reaction at the start called?
The initial rate
What data is gathered from a graph of the volume of gas collected against time for different concentrations of reactants? What can this be used to plot?
The initial rate (from the gradient at T=0)
This is then used to plot a graph of initial rate against concentration
What can a graph of initial rate against concentration to be used to work out?
What praportionalities / equations can be derived?
If the graph is a straight line then the concentration of a reactant is directly proportional to the rate.
rate ∝ [Reactant conc.]
or
rate = k[Reactant conc.]
What is the rate constant?
This is a measure of the rate of a reaction that is specific to a certain reaction at certain conditions
What affects the value of a rate constant for a reaction?
Temperature changes the value of the rate constant so it is important to state the temperature that the reaction, where the rate constant was determined, was conducted at.
Say if more than one reactant affects the rate of a reaction? What are the equations / praportionalities for that?
rate ∝ [Reactant1 conc.]
rate ∝ [Reactant2 conc.]
rate ∝ [Reactant1 conc.][Reactant2 conc.]
rate = k[Reactant1 conc.][Reactant2 conc.]
What is the concept of the order of the rate of a reaction?
This is how the concentration of a reactant affects the rate of a reactions.
What is a zero order reaction?
This is when the rate of a reaction is independent of the concentration of a reactant
e.g. rate ∝̸ [reactant conc.]
What is a first order reaction?
This is when the rate of a reaction is directly proportional to the concentration of a reactant
e.g. rate ∝ [reactant conc.]
What is a second order reaction?
This is when the rate of a reaction is directly proportional to the concentration of a reactant squared
e.g. rate ∝ [reactant conc.]^2
What is the order of a reaction when there are two first order reactants reacting? why?
Second order
The orders of the two reactants are added.
e.g. rate ∝ [reactant1 conc.][reactant2 conc.]
A + B ==> products
rate = k[A]^m[B]^n
m + n = order
What is the unit for the rate constant of a zero order reaction?
moldm^-3s^-1
What is the unit for the rate constant of a first order reaction?
s^-1
What is the unit for the rate constant of a second order reaction?
dm^3mol^-1s^-1
What is the use of the arrhenius equation? and why is it better than a standard rate equation?
It is used to show how the rate constant changes under different conditions
It is better than a rate equation because it takes into account other factors such as temperature and a catalyst
What is the Arrhenius equation (what is the equation for it)?
k = Ae^-Ea/RT
k = rate constant A = Frequency factor it is a constant taken across small temperature ranges Ea = Activation enthalpy (with the unit joules per mol) R = Gas constant T = Temperature in kelvin
How does the value of Ea change for a reaction?
The presence of a catalyst will change the value of Ea
How can the Arrhenius equation be rearranged and graphed?
It can be rearranged in the form: lnk = -Ea/R * 1/T + lnA This can then be graphed as y = m * x + c where: y = lnk m = -Ea/R x = 1/T c = lnA
What is the gradient and what is the y intercept for the graph of lnk (yaxis) against 1/T (xaxis)?
The gradient is -Ea/R
The y intercept is lnA
How can the gradient and the y intercept be used to work out values for A and Ea?
A can be calculated by rearranging the y intercept to find A. A = e^lnA Ea can be calculated by rearranging: gradient = -Ea/R to the equation: -gradient*R = Ea
How does the value of k OFTEN change with a 10C increase in temperature? (This is a rough general rule)
It doubles
How is the order of a reaction with multiple reactants found? What must be kept constant?
By conducting experiments where only the concentration of one reactant is varied at a time. The temperature must remain constant
For a reaction with multiple reactants, how can you keep the concentration of a one of them constant throughout the reaction? Why would you need to do this?
You would have the reactant not being measured in excess so that as it is used up its concentration doesn’t change by much during the reaction. This is important so that only one variable changes during the experiment.
What is a progress curve? What are its axis?
This is a curve showing how the concentration of a reactant (or product) changes over time.
yaxis - concentration of reactant / product
xaxis - time
What is the initial rate method? What is the method?
This is a method of finding the order of a reaction.
First multiple reactions are conducted with a single reactant varied in concentration each time.
Then the initial rate found using the gradient of a progress curve
Then all the initial rates are plotted on a graph of initial rate (yaxis) and concentration of reactant (xaxis)
The shape of the graph can show the order of the reaction
What is the shape of a graph of initial rate against concentration for a zero order reaction?
Flat straight line not passing through the origin
What is the shape of a graph of initial rate against concentration for a first order reaction?
Straight line through the origin
What is the shape of a graph of initial rate against concentration^2 for a second order reaction?
Straight line through the origin
What is the shape of a graph of initial rate against concentration for a second order reaction?
Curved line through the origin
How can the reciprocal of a reaction time be used to measure reaction order?
If the time taken for a certain quantity of product to form is calculated for different concentrations of a reactant then 1/time can be plotted against concentration and the shape of the graph can be used to work out reaction order.
The shapes produced are the same for the graph of initial rate against concentration
How can the half life of a reaction be used to work out the reaction order? Why is it useful?
This saves you from having to conduct multiple experiments as long as you know the concentration of a reactant as the reaction is progressing.
It works by producing a progress curve and then measuring the “half life”. If the half life is constant then the reaction is first order. If it is not a constant half life then the rate of a reaction is either zero order or first order.
What is half life when talking about rate and order?
It is the time that it takes for the concentration of a reactant to halve. e.g if it takes 10s to halve then at: T=0 1moldm^-3 T=10 0.5moldm^-3 T=20 0.25moldm^-3 T=40 0.125moldm^-3
What is the rate determining step?
For a reaction with multiple steps it is the step that is the slowest
How can the rate determining step be identified?
It is the step where the reactants are involved in the rate equation. Any reactants not involved in the rate equation are used in a step faster than the rate determining step.
How can the equation for the reaction of the rate determining step be calculated from a rate equation?
The order of the reaction for each reactant will tell you the number of moles of each reactant used in the rate determining step. This can then be used to work out the reaction mechanism for the rate determining step
What is one reason that the rate determining step will be slow?
The rate determining step might have a higher activation enthalpy so the number of molecules of reactant that can react may be low and cause a slower reaction
How can the rate determining step be seen on a reaction be seen on a enthalpy profile? What happens if multiple steps and intermediaries are shown on the profile?
It is the reaction with the highest activation enthalpy.
It is the reaction with the greatest difference in height.
Where can the rate determining step be found (in terms of order of the steps of a reaction)? How does this affect the reaction?
It can be any of the steps.
For the first step: it will cause the reaction to proceed slowly but any products formed from the first step will react much faster.
For the last step: It will cause a bottleneck and slow the reaction down.
What are two factors that need to be considered when trying to make the most economical operating conditions for a reaction?
The principles of equilibrium
The rate of a reaction
Discuss the ideal temperature and pressure for the following reaction:
C(s) + H2O(g) <=> CO(g) + H2(g)
ΔH+131kjmol^-1
Higher temperature
Lower pressure
Discuss the ideal temperature and pressure for the following reaction:
CO(g) + 2H2(g) <=> CH3OH(g)
ΔH-90kjmol^-1
Lower temperature
Higher pressure
Discuss the ideal temperature and pressure for the following reaction:
CH3OH(l) + CO(g) <=> CH3COOH(l)
ΔH-137kjmol^-1
Lower temperature
Higher pressure
What are the raw materials for chemical production called?
Feedstocks
How do raw materials become feedstocks? and why?
They have to go through chemical processes to ensure that they are pure, of the right concentration and of the right form
What are the 4 possible different outcomes of a reaction? (with regards to intended and unintended outcomes)
The reaction may form the desired product (singular)
The reaction may form the desired product and another undesired product (co-product)
A different (side) reaction may form one or more unintended products (by-product)
The reactants will remain unreacted
What is the name for a product produced in the correct reaction but is not the desired product?
This is a co-product
What is the name of products produced from an unintended reaction?
This are by-products
What are some costs associated to producing a chemical product?(4)
Research and development of reactions Plant design Plant construction Initial production Raw reactants
What is profit with regards to a chemical product?
This is the amount of money collected from the product after all the costs of producing that product are deducted
What is a fixed (or indirect) cost? Give 5 examples.
These are charges that are not affected by how much product is produced. These include: Labour cost Equipment and plant costs Research and development costs Plant design costs Land purchase etc
What is a variable cost? Give 3 examples.
These are costs that are affected by how much product is produced. This includes: Raw materials by-product disposal distribution costs
How does efficiency affect the total cost of production? Give examples.
Higher temperatures and pressure incur higher costs for equipment and energy.
However Better reaction conditions take less time and produce higher yields.
What is green chemistry?
This is a method of conducting chemical reactions so they are safer, more sustainable and better for the environment.
What are 2 great, inexpensive ways to produce a more economical reaction?
Adding a catalyst and recycling reactants
What are 2 ways that industry has conserved the heat of a reaction?
Pipes have been lagged to reduce heat loss and heat exchanges have been used to move heat from exothermic parts of reactions to other endothermic reactions
