Unit 1 Rates
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How do reactions happen
Reactions happen due to successful collisions between particles
How can reactions be followed
By measuring changes in concentration, mass and volume.
Measurement for a change in volume/time
Cm3s-1 or cm3/s
Measurement for change in mass/time
Gs-1 or g/s
What is a ‘reaction rate’?
The speed of rate of change of reactant to products
Can you think of 4 ways to speed up a chemical reaction
• increase temp • concentration • decrease particle size (increase surface area) • use a catalyst
Can you name two different ways to measure the rate of reaction?
Measure the mass lost of reactants The volume of gas produced of product or change of concentration
What is the calculation for average rate reactions
Change in measurable quality Average rate= —————————————— Change in time
Can you explain using collision theory why a reaction can be sped up (3)
• Decrease particle size, increases surface area and so more chances of successful collisions • Increase temperature, increases surface area kinetic energy of particles so more particles collide often • Increase concentration, increases number of particles so more chances of collisions.
Collisions theory- small surface area
The smaller the particle size, the higher the surface area. The higher the surface area, the greater the nu,her of collisions that can occur at any one time. The greater the number of collisions, the faster the reaction
Collision theory- higher concentration
The higher the concentration, the higher the number of particles. The higher the number of particles, the greater the chance of collisions that can occur. The greater the number of collisions, the faster the reaction.
Collision theory- high temperature
The higher the temperature, the higher the energy the particles have. The higher the energy, the faster the particles move. The faster the particles move, the greater the chance that they can collide. The greater the number of collisions, the faster the reaction.
What is a catalyst
A substance n that speeds up a reaction without getting used up itself
Why does temperature increase the rate reaction?
Increases the frequency of collisions
Why did most reactions start fast then get slower and slower?
The concentration of reactant molecules gets less and less
Why does a catalyst increase rate of reaction?
Provides a route with a lower activation energy