Section 7- The Chemical Industry Flashcards
(18 cards)
Equation for initial rate?
Amount of reactant used or product formed/time
k is the rate constant. What is the general trend with k’s size?
When is/isn’t k constant?
The larger k is the faster the reaction is.
It is constant for a certain reaction at a particular temperature, but it varies with temperature.
What is the only way you can find the order of reactions?
From experiments, no other way.
What does it mean if a concentration time graph is linear like y=-x and the derivative of it, rate concentration is a y=integer graph?
Would the reactant be included in the rate equation?
The reaction is zero order with respect to the reactant
No.
If the rate-concentration graph is a straight line graph and cuts through the origin, what order is the reaction with respect to the reactants concentration?
first order with respect to the reactant.
What is the half life in a reaction?
It is the time taken for the reactant to half in quantity.
How would you construct a concentration time graph (how would you find the results)?
You would consistently measure the concentration of a reactant in regular intervals. You would do this by taking regular samples from the reaction and quenching it (by adding a chemical or by cooling down the reaction significantly in order to stop it from progressing), and then you would construct a concentration-time graph. You would then extrapolate from the graph and would see whether the measurements were decreasing, remaining a constant, or increasing in gap.
What is the order of reaction with respect to X if the half life is:
Decreasing
remaining constant
increasing
Decreasing would mean zero order
Remaining constant would mean first order
Increasing would mean second order or more.
How could you calculate k using a method if you dont have the respective rates and concentrations?
k= ln2/t^(1/2)
The rate constant (k) is affected by temperature. What equation links activation enthalpy and the rate constant?
What would the axis be?
The arrhenius equation:
lnk=-Ea/RT +lnA
The axis would be:
x axis- 1/T
y axis- lnk
The rate determining step is the ____ step in a multi step reaction
Slowest
What can you predict from the following:
The rate determining step
The rate equation. The order of reaction with respect to a reactant can tell you the number of molecules of a reactant within the rate determining step and vice versa.
rate=k[X]^2 [Y]
2[X] + [Y] –> XY
What costs need to be considered when producing a chemical?
How would scientists decide the conditions of their industrial process?
The cost of raw materials, the cost of fuel, the cost of material disposal, as well as overhead costs (such as staff wages etc).
They would need to choose conditions which would promote a high atom economy and yield, which minimises cost (for maximised profits), whilst considering the environmental impact of the process. For example, reactions which require very high temperatures and pressures are very expensive to maintain, and often require fossil fuels to power. Reactions with the highest atom economies and the highest percentage yields are the best because they have the fewest waste products.
How do the following effect the equilibrium constant:
Temperature
Pressure
Catalyst
Temperature is the only one which effects the value of Kc, because it will favour the side of the reaction which is endothermic if the temperature increases, and the side which is exothermic if the temperature decreases, Kc value changes.
Pressure has no effect on Kc, but it effects the position of equilibrium. If it increases, the position of equilibrium will shift to the side of reaction which has the fewest moles of gas, Vice versa.
A catalyst has no effect on the magnitude of Kc, nor the position of equilibrium. It simply speeds up the rate at which the forward and backward reactions occur, and therefore the rate at which dynamic equilibrium is achieved.
The position of equilibrium effects how economical something is. Go into detail about this in terms of pressure, and temperature, and the use of catalysts. Use the haber process as an example
In the haber process, the conditions are as follows:
400 degrees
200 atmospheres
Iron catalyst
The forward reaction is exothermic and the number of moles of gas is greater on the left hand position.
Increasing the temperature increases the rate of reaction, because all the molecules within the reaction have more kinetic energy, and a greater proportion of molecules are therefore able to react upon collision. However, the position of equilibrium shifts left, so this decreases the yield of ammonia. But a high temperature is needed or else the reaction will occur too slowly to be economically viable.
A higher pressure is useful here as it too increases the rate of reaction by decreasing the space available for the moelcules to move and therefore making it more likely for collisions to occur. It also shifts the equilibrium to favour the position of ammonia, and increases the yield of ammonia. However, increasing the pressure is very expensive and dangerous to maintain, so this is rather a compromise.
How could you experimentally find the concentrations of substances at equilibrium?
If the substance is coloured, you could plot a calibration curve of absorbance against concentration with known absorbance values. You could then take absorbance reading of the reaction regularly until there is no change in absorbance value. You can then extrapolate the absorbance to find the concentration of the reactant at equilibrium. This will work although there is other reactants within the mixture because you will have a complementary colour filter to the colour of the reactant you are measuring in the colourimeter and the other molecule colours will be reflected and not therefore interpreted by the colourimeter.
If one of the substances youre measuring is acidic or basic, you can use a pH probe to measure any changes in pH, until the pH remains constant. You could then use Ka/-log10 to calculate various things from then.
What are the colours of the following nitrogen compounds:
NO
N2O
NO2
Colourless
Colourless, this is laughing gas, has a sweet taste. This is also used as a recreational drug, and youve never seen someone exhaling brown gas so it has to be colourless.
Brown. Has a sharp odour and is toxic. If you think shit brown is toxic.
What are tests involving:
Ammonium compounds
Nitrate Ions
Ammonium compounds react in the presence of sodium hydroxide to form Ammonia and water. This can be tested with damp red litmus paper turning blue.
NH4+ + OH- —> NH3 + H2O
Nitrate (V) ions react in the presence of Devardas alloy to produce ammonia gas. this can be tested with damp red litmus paper which turns blue.
