C7.1 - Chemical reactions
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Collision theory explains
why reactions occur and why they occur at different rates
For chemical reaction to occur
the reacting particles must collide with enough energy
The energy involved in collision must be
enough to break the chemical bonds
The minimum amount of energy required in collision is called
activation energy
Activation energy is
the minimum energy in which particles must collide in order to cause a chemical reaction
The rate of reaction is
the speed of a reaction
To increase the rate of reaction we need to increase
the “frequency” (word should be used in exam) collisions and/or the energy of the reactant particles
4 factors that affect rate of reaction are
Temperature Concentration Pressure (for gases) Surface area
Increasing the concentration of dissolved reactants increases
the frequency of collisions as there are more particles in the same space which increases rate of reaction
increasing pressure increases
the frequency of collisions which increases rate of reaction
Increasing temperature increases frequency of collisions because
more heat in a particle transfers to more kinetic energy into the particle meaning it will move faster so more collisions will occur each second. They will also have more energy than the activation energy required.
Increasing surface area increases rate of reaction because
if there is more surface area than more particles can collide in which this is often done by breaking up solids into smaller lumps so that there is more exposure of a particle.
We can increase surface area by making substances into powders but some are dangerous like:
flour mills and coal mines which can be flammable and start a chain of explosive reactions
Catalysts are substances that
speed up a reaction without getting used up
catalysts increase/decrease rate of reaction
increase
How can we investigate changing surface area affecting rate of reaction
by measuring how much gas is produced when marble chips (calcium carbonate) of different surface areas react to HCI
method and apparatus needed for marble experiment
apparatus: Conical flask, delivery tube, gas syringe, HCI and marble chips Method: Place different surface area marbles into the flask Put it excess amounts of HCI Start the timer Record the volume of gas produced every 5 seconds IV: different surface area marbles DV: Volume of gas produced every 5 seconds CV: Same volume of HCI, same finish time and same mass of marbles
What does the graph of the marble experiment look like and what is the general trend
the rate of reaction decreases as the reaction proceeds. At first the rate of reaction is at its highest with lots of particle collision. But as time goes on the rate slowly decreases until it eventually plateau’s.
How do we investigate changing concentration and how that affects rate of reaction
by observing a color change in the reaction between sodium thiosulfate and HCI
What is the apparatus and method for the change of color experiment
apparatus: A beaker/conical flask, HCI, measuring cylinder, sodium thiosulfate, a sheet of paper and a pen/pencil Method: Put an X on a sheet of paper and put it under the beaker/conical flask Place the solution of sodium thiosulfate in the beaker Pour in the amount of known HCI into the beaker Start the stopwatch Stop the stopwatch when the X is no longer visible Repeat for different volumes of HCI IV: The volume of HCI placed in beaker DV: time taken for X to disappear CV: Same volume of sodium thiosulfate
What does the graph of color change look like
As you increase the volume of HCI the rate of reaction increases so the curve will be steeper with a more higher concentration than a curve with less.
How to interpret a rate of reaction graph
If the graph is steeper the reaction is faster and if the graph plateau’s or is flat the reaction is completed or stopped