2.2 Flashcards
What is rate of reaction
Change in concentration of a reactant or product per unit time
Equation and units for rate in concentration terms
Rate = change in conc/time Units = mol dm-3 s-1
When is the rate of reaction usually fastest
Start of reaction
Each reactant has its greatest concentration
Why does rate slow down as the reaction proceeds
Concentration of reactants decreases
When does the rate of reaction become 0
When the reaction stops
When trying to calculate initial rate from a graph what do you do
Find the gradient of the tangent
Factors affecting reaction rates
- concentration of a solution
- surface area of a solid
- temperature of a reaction
- catalyst
- light
What is activation energy
Minimum energy required to start a reaction by breaking bonds
What do energy profiles compare
Enthalpy of the reactants with the enthalpy of the products
Look
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Effect of concentration on reaction rates
- increase in reactant concentration = increase in reaction rate
- more molecules in the same volume so distance between molecules is reduced and theres an increase in the number of collisions per unit time
- greater change of collisions with at least the activation energy and so rate increases
- gaseous reaction - increasing pressure has the same effect
Effect of surface area on rate of reaction
• reducing the particle size increases surface area and increases the rate of reaction
Effect of temperature on reaction rates
- temperature increase = reaction rate increases
- molecules have more kinetic energy and are moving faster
- more molecules have energy that is greater than the activation energy so more collisions take place in a certain length of time
Effect of higher temperature on Boltzmann energy distribution curves
- Peak moves right with a lower height
* more molecules have sufficient energy to react so increases rate significantly