Kinetics and equilibrium Flashcards
What is meant by the term activation energy
The minimum energy needed for a succesful reaction to occur or a succesful collision to occur
Why at a fixed temp does the rate of a reaction double when the conc doubles
As there are now twice the number of particles in a given volume so twice the number of collisions/ higher collision frequency
Why is it possible to use a simplified formula as a measure of the rate of reaction
As it is a fixed value there is a fixed endpoint
Give one reason why the reaction between hydrogen and chlorine is very slow at rtp
As not many particles have enough energy to react (Ea)
Explain why a small increase in temp can lead to a large increase in ror between h and cl
As MANY momre particles have an energy in excess of Ea so higher succesful collisions
Explain effect of increasing conc on..
More FREQUENT succesful collisions
Explain when equilibrium is reached
When the concentrations are CONSTANT not the same bc their different its when they are constant and level off
Use le chateliers principle to state whether a …
High as fwd reac is so using a higher temp = favour the forward reac, producing a higher yield of hydrogen at high temps the equilibrium shifts to the right to oppose the increase in temp.
Why is high operating pressure used in industry
As the reaction gets to equilibrium faster so more particles in a given vol so increased collision frequency
Explain why the catalyst is more effective when coated onto an unreactive honeycomb
As there is a bigger surface area so more effective collisions
Will there be any chance of yield if there are the same number of moles on both side with pressure
No make sure you check
State the effect if any on the value of kc of adding more hydrogen to the equilibrium mixture
No effect- only temp changes kc not conc or whatever.
Define enthalpy change
The heat or energy change at constant pressure
Define hess’ law
The enthalpy change is independent of the route taken
Define the standard enthalpy change of formation
The enthalpy change at constant pressure when 1 mole of a compound is formed from its constituent elements with all the reactants and products in their standard states.
Why can a value of something not be zero
As it is not in its standard state
Why is the standard enthalpy of formation of barium and aluminium both zero
As they are both elements
Why can an experiment have a much smaller experimental error
Due to a lower heat loss
Define the term standard enthalpy of combustion
The enthalpy change when 1 mol of a compound is completely burnt in oxygen under standard conditions
Define rate of reaction
The of change of concentration of a substance in a given unit of time
If they ask you what is happening to w if its a straight line
The rate is zero as all the… eg mg has reacted or been used up
If your working out the moles using the q/n thing what do i need to remember
If you have the q firstly make sure convert into kj. And if they give you a neutralisation value eg -51kj make it positive and do the kj/51
If they want you to find out the minimum conc of something mo/vo
So do the moles divided by v make sure you divide by 1000 in dm3
Suggest one possible risk to a person who uses a hand warmer containing sodium hydroxide and hcl
The container can split releasing corrosive chemicals, can burn hands
(Forward reaction is endothermic)
Use le chateliers principle to state whether a high or low temp should be used to obtain the highest possible equilibrium of yield on the right
Increase temp- the forward reac is endothermic so at high temps the equilbrium will shift to the right ABSORBING HEAT COOLING DOWN THE REACTION to oppose the increase in temp.
The carboxylic acid is very expensive and ethanol is inexpensive. The mole ratio is 1:10- why
So as we increase the conc of ethanol the equilbrium shifts position to the right side to oppose this shift in conc increasing the yield of the product.
State le chateliers principle
When a system is at equilibrium and a factor is changed the position of equilibrium will shift to oppose this change. HAVE TO SAY EQUILIBRIUM CANNOT USE SYSTEM ALONE
Give one reason why the reaction between hydrogen and chlorine is very slow at rtp
As very few particles have sufficient energy to react. High ea
Suggest one reason why a solid catalyst for a gas phase reaction is often in the form of a powder
Increases sa
Suggest a reason why the catalyst must be hot
To overcome activation energy
Suggest why at a constant temp most of g eventually decomposes
As molecules gain energy due to collisions
What does the area under the curve represent
The total number of molecules in the sample.
State why this curve starts at the origin
As no molecules have no energy
Explain why the rate of reac decreases w time
As fewer collisions as w is used up
Explain the process that causes some molecules in this sample to have very low energies
Collisions as some molecules slow down losing energy
Explain why this reaction is described as a homogenous reaction
All the reagents are in the same phase.
State the property of so2 that cause pollution when it enters rivers
Acidity or produces h+ ions
why must a catalyst be hot and why does it remain hot
To overcome the activation energy and it stays hot as the reaction is exothermic and so releases heat
How would you change iron in the hand warmer to make sure it stays warmer for longer
Increase the size of iron so decrease the surface area so less of the iron reacts, reacts slower
Pure magnesium reacts completely with an excess of dilute sulfuric acid and is very rapid initially. This reaction slows down and stops before all of the calcium has reacted. Use your knowledge of the solubilities of group 2 sulfates to explain why these reactions of mg and calcium w dilute sulfuric acid are so different
As mag sulfate is soluble and calcium sulfate is insoluble the calcium is coated w sulfate which prevents further reaction w the acid
Predict the effect of kc if the reaction is carried out at a lower temp
Increase
At any time, most of the molecules of G have energy less than the activation energy.
Suggest why, at a constant temperature, most of G eventually decomposes.
Molecules gain energy (or always some molecules have E > Ea) 1
Due to collisions
State the effect, if any, of adding a catalyst on the time required for G to decompose,
compared with a similar sample without a catalyst. Explain in general terms how the
catalyst has this effect.
Time for decomposition ………………………………………………………………………………..
Explanation ………
Decreases 1
Ea lowered (1)
By alternative route (1)
So more molecules have energy > Ea
State why this curve starts at the origin
No molecules have no energy
OR all molecules have some energy
The rate of a chemical reaction may be increased by an increase in reactant
concentration, by an increase in temperature and by the addition of a catalyst.
State which, if any, of these changes involves a different activation energy. Explain
your answer.
Change(s) ………………………………………………………………………………………..
Explanation …
Changes: Catalyst (1)
Explanation: Alternative route (1), with a lower activation energy (1)
OR a lower activation energy (1)
so more molecules can react (1)/more molecules have this energy
suggest why a catalyst may become less efficient if the co2 and hydrogen contain impurities
as impurities block active sites
