C2.4 Flashcards
What is a catalyst?
A substance that increases the rate of a chemical reaction without being altered or used up
What are the factors that affect the rate of a reaction?
~ Temperature ~ Concentration of solutions ~ Pressure of gases ~ Surface area of solids ~ Use of a catalyst
What is the activation energy?
The minimum amount of energy required to cause a reaction
What are the particles like in a low temperature mixture?
~ Move slow
~ Less collisions as they have less energy so less particles can collide successfully
What are the particles like in a high temperature mixture?
~ Move fast
~ More collisions as they have more energy so more particles can collide successfully
What causes chemical reactions?
Reacting particles colliding with each other with sufficient energy
What are the particles like in low concentrations?
~ Less of them in that volume
~ Spread out
~ Less collisions
What are the particles like in high concentrations?
~ More of them in that volume
~ Close together
~ More collisions
What unit are concentrations of solutions given in?
Mol/dm^3
What does a decrease in surface area of a solid mean?
~ Fewer particles so less successful collisions
~ Less collisions = slower reaction
What does an increase in surface area of a solid mean?
~ More particles so more successful collisions
~ More collisions = faster reaction
What do catalysts lower?
The activation energy
What’s one way that a catalyst lowers the activation energy?
By providing a surface for molecules to attach to, therefore increasing the chance of them colliding
What are some processes that involve catalysts?
~ Cracking hydrocarbons
~ The manufacture of ammonia
Why is increasing the rate of chemical reactions important in industry?
Because it helps to reduce costs
What does lowering the activation energy mean for the industry?
Reactions can happen at a lower temperature, which reduces costs
How can the rate of a chemical reaction be found?
Time
How could you measure the amount of product formed in a decomposition reaction?
~ Weighing the mixture before and after the reaction
~ Or using a gas syringe to measure the volume of gas produced
What is the test for oxygen?
Inserting a glowing splint into a jar of collected gas which will relight in the presence of oxygen
Why could one reaction be faster than another?
It could have... ~ A greater surface area ~ A higher temperature ~ A higher concentration ~ Used a catalyst
How do measure the rate of reaction between acid and sodium thiosulphate?
By drawing a cross on paper, placing it under the glass and measuring the time it takes to disappear
(The solution goes from clear to cloudy)
What happens when the reactants have been used up?
The volume of gas/mass of product collected will stay the same (a horizontal line on a graph)
What does increasing the pressure do to the particles?
~ It reduces the space they have
~ Particles are closer together
~ More successful collisions
What are some examples of a catalyst?
~ Manganese oxide
~ Iron
~ Platinum
~ Nickel
What’s a problem with increasing the temperature or pressure to speed up a reaction?
Costs money
Different catalysts are used…
…for different reactions
What are advantages of using catalysts?
~ Less energy used ~ Speeds up reactions ~ Reusable ~ Lower production cost ~ Only needed in small amounts
What are disadvantages of using catalysts?
~ Can be toxic
~ Can be expensive
Why do powders react faster than larger pieces of solid?
Because they have a larger surface area to volume relation
What does a gas syringe measure?
The volume of gas produced
