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AQA Chemistry Y1 Revision > Kinetics > Flashcards

Flashcards in Kinetics Deck (28):

What is rate of reaction?

Rate of reaction is the change in the amount of reactant or product over time.


What conditions are required in order to make particles react when they collide?

The particles must collide in the right direction

They must collide with at least a certain minimum amount of energy


What is the minimum amount of kinetic energy particles need to react with called?

Activation energy


What does activation energy do?

Break the bonds between reactant particles


What does the area under the Maxwell and boltzmann diagram show?

The total number of molecules in the reaction.


What does the peak of the Maxwell -boltzmann diagram show?

The most likely energy for any single molecule.


where does the Maxwell-boltzman diagram always start?

the diagram always starts at 0,0 because 0 molecules have 0 energy


What is the effect of increasing temperature on the rate of reaction?

If you increase the temperature more particles have at least the activation energy hence more molecules are ready to participate in collisions. Plus each molecule will have more kinetic energy so will be moving around more thus there are more collisions.


What will increase the temperature of a reaction do to the Maxwell and Boltzmann diagram?

The Maxwell and Boltzmann diagram will change by shifting too the right, the total number of molecules will be the same so the area under the graph should be the same.


What will decreasing the temperature do to the Maxwell and Boltzmann diagram?

The curve will shift to the left as there will be less molecules with the required activation energy.


How does changing the concentration affect the Maxwell and Boltzmann diagram?

The area under the curve gets bigger as there are more particles, the particles are closer together in the same volume so collisions - thus chances for particles to react- are more frequent. If there are more molecules there will be a chance that there are more molecules with the required activation energy.


How will increasing the pressure of a reaction that involves gasses effect the rate of reaction?

Increasing the pressure will mean that particles are closer together therefore there will be a greater chance of collisions which will mean a faster rate of reaction.


What is a catalyst used for?

To increase the speed of a reaction


How does a catalyst speed up the rate of reaction ?

A catalyst provides an alternative reaction pathway with a lower activation energy.


Is a catalyst changed as result of being used in a reaction?

At the end of a reaction a catalyst is chemically unchanged.


Catalysts are not used up in a reaction what is a benefit of this?

A small amount of catalyst can catalyse a huge reaction.


If a catalyst is used in a reaction how is the Maxwell and Boltzmann diagram affected?

The shaded region of particles with the activated energy will be larger as there will be more particles with the activation energy as the activation energy is lower hence more particles will have it.


Whats the equation for rate of reaction?

Amount of reactant used or Amount of product formed


Briefly - what methods can be used to measure rate of reaction?

- Conical flask on top of white tile with black mark on it

- Change in Mass

- Gas volume given off


When would you use the white tile method when measuring rates of reaction?

When the reaction involves the formation of a precipitate


When would you use the change in mass method of measuring a rate of reaction ?

When a product is a gas


When would you use the volume of mass given off method for measuring rate of reaction?

When the product is a gas


Explain the white tile method for measuring rate of reaction

1) You stand a conical flask on top of a white tile that has black mark on it.
2)you then add your reactants to the conical flask and start the stopwatch
3)as the precipitate forms the mark will become harder to see , when the mark can no longer be seen stop the timer
4)the reading on the timer is how long it took the precipitate to form
5) this could then be compared with other results investigated with different variables.


What are the draw backs off the white tile method - used to measure rates of reaction?

The idea of when the black marks on the white tile have disappeared is subjective. People may not a free exactly when the mark has "disappeared".


Explain the change in mass method for measuring rate of reaction.

A conical flask is placed on a mass balance , the reactants are poured or put into the flask and a timer is started , you draw a table with one column reading time and the other mass , over equal increments of time you measure the mass of the reaction mixture until you get concordant results for mass which shows the reaction has reached its end point.


What are the drawbacks of the mass balance method of measuring rates of reaction ?

The method releases gasses into the air , these gases could be toxic or flammable so it is best to carry out the experiment in a fume cupboard.


Explain the measuring the volume of gas evolved method for calculating rate of reaction ?

In this method you use a gas syringe you put the reactants into a conical flask and bung the top with the cork that is connected with secure seals to avoid gas escaping to the gas syringe , you start the timer. You then read of the volume of gas evolved at equal time increments , you know that the reaction has finished when the volume stops increasing. The method is accurate as the mass syringe gives accurate measurements and no toxic or flammable gas escapes into the room it is collected in the syringe.


What is a draw back of the gas syringe method for measuring rate of reaction?

If too much gas is evolved then the gas syringe won't be able to measure it , plus gas syringes are quite expensive.