Rate of Reaction Flashcards
What does a chemical reaction’s rate tell us?
Tells us how quickly reactants are converted into products.
Why are faster reactions often the best?
They yield more product in a given amount of time.
How do we plot reaction rates on a graph?
Rates of reactions at specific times can be calculated using graphs:
Draw a tangent to the curve (a straight line that touches the curve at just 1 point).
Work out the tangent’s gradient:
Rate of reaction = change in y/change in x
What does collision theory explain?
How reactions happen and why they happen at different rates.
What is activation energy?
The minimum amount of energy required in a chemical reaction.
How can we increase the rate of reaction?
By increasing the frequency of collisions and/or the energy of reactant particles. This can be achieved by changing lots of different factors.
What are the main factors that affect the rate of chemical reactions?
- Concentration of dissolved reactants
Increasing the concentration increases the collision frequency. This increases the rate of reaction.
- Pressure of gas reactants
Increasing pressure is like increasing the concentration.
It has the same outcome of increasing the collision frequency, which increases the rate of reaction. - Temperature
Increasing the temperature increases the rate at which collisions happen.
Increasing the temperature increases the energy of reactant particles. This means that a greater proportion of the particles will have more energy than the activation energy that is needed.
Together, these lead to more successful collisions. This increases the rate of reaction. - Surface area of solid reactants
Increasing the surface area increases the collision frequency. This increases the rate of reaction.
This is often done by breaking up solids into smaller lumps (e.g. powders).
This increase in surface area to volume ratio makes sure that more particles are exposed to attack. - Catalysts
Substances that increase a chemical reaction’s rate without reducing in quantity during the reaction are called catalysts.
What are some advantages of catalysts?
Cost-effective
Despite the fact that some catalysts are expensive precious metals (e.g. platinum and palladium), they are often cost-effective to use.
This is because a small amount can speed up a reaction by a lot. It may be cheaper to pay for the catalyst at the start and increase the rate of reaction after that.
Paying for a catalyst may be cheaper than paying for the energy needed to increase either temperature or pressure.
Reduced burning of fossil fuels
By reducing the necessary temperatures and/or pressures, fewer fossil fuels need to be burned.
This means that we can reduce our negative environmental impact.
What is a disadvantage of catalysts?
Many catalysts are toxic (e.g transition metals), and these can escape into the environment and contaminate ecosystems.
Are catalysts use chemical equations?
No
