Rates, Equilibria and Haber Process

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What is the rate of reaction and unit?
Change in concentration per unit time and moldm^-3s^-1
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What is a technique to measure the rate of reaction?
Change in mass/volume/colour over time
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What is collision theory?
For 2 substances to react, collisions between particles must be successful - unsuccessful also occurs
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What conditions need to be met for a successful collision?
1. Molecules have energy > or equal to Activation Energy
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How does increasing the concentration increase the R.O.R?
More particles per unit volume so more successful collisions per second.
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..?.. the pressure of gas increases the rate if reaction. Why?
Increasing - more particles per unit volume so more successful collisions per second
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Why does greater surface area mean faster rate of reaction?
more particles exposed to reactants so more successful collisions per second
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What does the Boltzman distribution show?
Distribution of energies of particles within a sample
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What is on the x and y axis of a Boltzman distribution and what does the area under the graph represent?
x - energy, y - number of particles, area - total number of particles
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Why does higher temp = Higher R.O.R?
Higher temp means more particles have Activation energy or above so more successful collisions per second
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How does Boltzman Distribution change for higher temperature?
Peak lower and right side of graph higher
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What is a catalyst and how does it work?
Substance that speeds up reaction (by providing alternative route with lower activation energy) without being used
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What values don't change when catalyst is used?
Delta-H and product yield
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How does Boltzman distribution change when catalyst is used?
Activation energy lower (further left)
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What are two types of catalyst used?
Homogenous - same physical state as reactant, Heterogenous - different physical state as reactants
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What are three benefits of catalysts?
Lower temp and pressures so less energy required, so less fuels burnt so less CO2, increases atom economy so fewer pollutants, benefits to environment + improved sustainability outweigh potential toxicity of some catalysts.
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What are steps involved in heterogenous catalysis?
Absorption, chemical reaction and desorption
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Describe Absorption
Reactants absorb to surface of catalyst
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Describe chemical reaction
Absorption weakens bonds and lower Ea, chemical reaction takes place
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Describe desorption
Product leaves surface of catalyst
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What is equilibrium sign?
Top half forward arrow, bottom half backwards arrow
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What does dynamic equilibrium mean?
Forward and backward reaction both occurring and are balanced
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What are 2 features of dynamic equilibrium?
1. Rate of forward reaction = rate of backwards, 2. conc of reacts and products will remain constant unless conditions are changed
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Equilibrium needs to be in a ..?.. system so reactants and products ..?.. escape
Closed, Can't
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State Le Chatelier's principal
If a system in equilibrium is subject to change, it will move in a direction to oppose change
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What 3 changes cause change in position of equilibrium?
Concentration, pressure and temperature
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If number of gas moles is equal on both sides, what will an increase in pressure do?
Just increase rate of reaction
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If temp is increased will equilibrium position go to to exothermic or endothermic reaction? Why?
Endothermic as that absorbs energy so reduces termperature
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What is a homogenous system?
One where the products and reactants are all the same state
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In the equilibrium equation, what side of the sign is on the top?
Right
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In the equation for equilibrium constant, what do the capital letters stand for?
Concentration of reactant/product
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In the equation for equilibrium constant, what do the lower case letters stand for?
The stoichiometric coefficient of the reactant/product in the balanced equation
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Kc (equilibrium constant) is when concentrations are in what unit?
moldm^-3
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Kc (equilibrium constant) is at what condition?
Constant temperature
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What does Kc (equilibrium constant) value tell us?
The relative amounts of products and reactants and equilibrium
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A large ( >1) equilibrium constant (Kc) means the equilibrium position is to the ..?..
Right
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A small (
Left
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If the equilibrium constant is 1 what does this tell us?
The equilibrium position is halfway between reactants and products
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Why do you use compromising conditions in Haber process?
In order to balance yield of ammonia, the rate at which it is produced and the cost of the plant and energy
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Why is pressure of 200 atm used in Haber process?
increases rate of forward reaction but can't go higher as safety laws are very strict
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Why is temperature of 400 -450 degrees celsius used?
Although it compromises equilibrium yield, it increases the rate of reaction in general
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Why is iron catalyst used?
Speed up rate of reaction without being used
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Why is unreacted hydrogen gas recycled?
To reduce waste from reaction
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Other cards in this set

Card 2

Front

What is a technique to measure the rate of reaction?

Back

Change in mass/volume/colour over time

Card 3

Front

What is collision theory?

Back

Preview of the front of card 3

Card 4

Front

What conditions need to be met for a successful collision?

Back

Preview of the front of card 4

Card 5

Front

How does increasing the concentration increase the R.O.R?

Back

Preview of the front of card 5
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