CHEM Topic 6 + 16 Chemical Kinetics

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36 Terms

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chemical kinetics
the study of rates of chemical reactions and the mechanisms by which a chemical reaction takes place
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rate of reaction
the speed at which reactants are used up or products are formed
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reaction rate
change in concentration over time
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collision theory

1. the reactant particles must collide with each other
2. the collisions must be of enough energy to overcome the activation energy
3. the collisions must occur with correct geometrical alignment/orientation (= steric factor)
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activation energy
the minimum energy required by the reactants to bring about a chemical reaction
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factors to change reaction rate
* increase number of collisions between reactant particles
* increase energy of collisions
* decrease activation energy
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catalyst
substance that accelerates the rate of reaction by lowering the activation energy without being consumed/used up
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homogenous catalyst
acts in the same state as reactant
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heterogenous catalyst
acts in different state to reactant
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measuring changes in concentration
* changes in pH (acid-base reactions)
* changes in conductivity (in electrolytes)
* changes in mass/volume of solids or gases
* changes in colour (transition metals or coloured compounds)
* graph change in concentration/time (slope of tangent)
* measure rate of gas produced
* measure time for colour to change
* measure how fast reactants used up
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electrical conductivity
* presence of ions allows a solution to conduct
* reaction rate can be found from changes in conductivity
* conductivity probe
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titration
allows measuring the change in volume as reaction progresses

titration apparatus
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pH
* not ideal method because dealing with small changes in concentration over pH scale
* useful if change in \[H+\] or \[OH-\]
* pH probe
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light absorption/change in colour
* if reaction produced precipitate: able to time how long it takes formation of product to cloud view of mark made on piece of paper placed under reaction vessel
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spectrophotometer
* measures wavelength of colour forming solution
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colorimeter
filters out a specific colour
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Br2
brown
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I2(s)
violet
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I2(g)
light yellow
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KMnO4
dark purple
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individual order
the power to which initial concentration is raised in the rate equation
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overall order
the sum of all the individual orders in the rate equation
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contact process
industrial method for the production of sulfuric acid using a catalyst
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half life of a reaction
the time required for half of the reactants to react
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0 order half life
decreases
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1st order half life
constant
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2nd order half life
increases
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1st order units of rate constant (k)
s-1
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2nd order units of rate constant (k)
s-1 mol-1 dm3
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3rd order units of rate constant (k)
s-1 mol-2 dm6
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unimolecular
single molecule involved in an elementary step
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bimolecular
two molecules or atoms involved in collision in an elementary step
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termolecular
three molecules or atoms involved in collision in an elementary step
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intermediate
a species that is formed from the reactants in a chemical reaction which then goes on to react further to form the products
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transition state/activated complex
* highest energy state = indicates point at which new bonds are being formed + old bonds being broken
* highly unstable
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rate determining step
* step with the highest activation energy
* slow step