Reaction rates Flashcards
Importance of controlling a chemical reaction
If a reaction is too slow then it is not economically profitable, if the reaction is too fast there is a risk of explosion.
Conditions necessary for a chemical reaction to take place
Collisions between reactant particles occur.
Sufficient collision energy to reach or surpass the activation energy
Good collision geometry
Factors affecting the rate of reaction
Concentration
Temperature
Particle size
Catalyst
Difference between particle size and surface area
Particle size is where the reactants are broken apart into smaller pieces. Surface area is the area on the surface of the reactant.
Increase in surface area means a decrease in particle size
Vice versa.
Relative rate of reaction formula
RR = 1/t
Temperature explain on relative rate
As the temperature increases the average kinetic energy increases, meaning collisions occur with more energy, meaning there is a larger number of particles equalling or surpassing the activation energy and the reactant particles collide faster, increasing the frequency of collisions. Therefore the rate of reaction increases
Amount of temperature increase to double a rate of reaction
10 degrees Celsius
Particle size rate of reaction explain
As the particle size decreases the surface area increases, meaning there is more area for reactant particles to collide, meaning that reactant particles collide more frequently, therefore increasing the rate of reaction
Concentration explain rate of reaction
As the concentration increases the number of reactant particles increases, meaning that the reactant particles collide more frequently. Therefore the rate of reaction increases.
Catalyst explain on the rate of reaction
A catalyst provides an alternative energy pathway, with a lower activation energy.
Activated complex definition
The unstable arrangement of atoms formed at the maximum of the potential energy barrier.
What happens at an Activated complex
The intramolecular bonds between reactant atoms begin to break down and new intramolecular bonds begin to form to produce products.
Activation energy definition
The minimum energy required by colliding particles to form an activated complex.
Potential energy diagram
A graph which shows the potential energy of the reactant particles, activated complex and product particles.
Potential energy diagram axis
X axis is reaction pathway
Y axis is potential energy (kJmol-1)
Activation energy symbol
Ea
How do you calculate the activation energy
Difference between reactants and activated complex/
Difference between the products and activated complex
Enthalpy definition
The is the measure of chemical energy stored in substances,
Collision geometry importance
Particles must collide with correct collision geometry to form an activated complex.
Where is the activated complex found on a potential energy diagram.
At the top of the curve.
Catalyst effect on the activation energy
The catalyst decreases the activation energy.
Calculating enthalpy formula
Delta H = EH(products) - EH(reactants)
(Products minus reactants)
How do you know if a reaction is exothermic on a potential energy diagram
The enthalpy is negative
How do you know if a reaction is
How do you know if a reaction is endothermic
The enthalpy is positive
Endothermic reaction definition
A reaction where the product molecules contain more potential energy than the reactants, meaning heat energy is absorbed.
Exothermic reaction definition
A chemical reaction where the product molecules contain less potential energy than the reactant molecules, meaning the reaction gives out heat energy.
Energy distribution diagram
The graph which shows the number of particles and the energy of the particles.
Energy distribution diagram axis
X - kinetic energy
Y- number of particles /collisions
Temperature effect on an energy distribution diagram
Increases the width of the graph by increasing the kinetic energy
Decreases the number of collisions/particles slightly due to increase in kinetic energy.
The hump gets wider and shorter.
Catalyst effect on an energy distribution diagram
Moves the activation energy left, so more particles are reaching the activation energy.
Temperature definition
The average kinetic energy of particles in a substance.
Constants in reaction rates experiments
Concentration
Temperature
Volume/ pressure
Particle size
Concentration experiment
Sodium thiosulphate plus hydrochloric acid, measure the rate of reaction and repeat with more water diluted in each time. The reaction goes cloudy so put a cross down below the beaker.
Temperature experiment
Potassium permanganate + sulphuric acid, the mixture goes from purple to colourless, should record rate of reaction and then repeat with higher temperature.
