Rates of Reaction and Reversible Reactions Flashcards
(54 cards)
What is the rate of a chemical reaction?
Speed at which reactants turn into products.
Give examples of slow, moderate, and fast reactions.
- Slow: Rusting of iron
- Moderate: Magnesium + acid
- Fast: Burning
- Very fast: Explosions
How can reaction rate be measured?
- Measure amount of product formed or reactant used over time
- Steeper graph = faster rate
- Flat line = reaction finished
What does collision theory say about reaction rates?
- More frequent collisions = faster rate
- Collisions must have enough energy (activation energy) to be successful
What is activation energy?
Minimum energy needed for particles to react.
What factors increase the rate of reaction?
- Higher temperature
- Higher concentration (or pressure)
- Greater surface area
- Use of a catalyst
How does temperature affect rate?
- Increased temp
- Particles move faster → more collisions
- Increased energy of collisions -> particles re moving faster
- Reactions only happen if the particles collide with enough energy
- More successful collisions per unit time
- Increased rate
How does concentration affect rate?
- Solution more concentrated
- More particles of reactant in the same volume
- Collisions more likely
- Increased rate
How does pressure affect rate?
- Increasing pressure
- Particles are more crowded
- Frequency of collisions between particles will increase
- Increased rate
How does surface area affect rate?
- Smaller particles = larger surface area to volume ratio
- Particles have more area to work on
- Frequency of collisions increase
- Increased rate
What is a catalyst?
A substance that increases the rate of a reaction without being chemically changed or used up.
Does a catalyst affect the products of a reaction?
No, it doesn’t change the products — the reaction equation stays the same.
Why is only a small amount of catalyst needed?
Because it isn’t used up, you only need a tiny bit to catalyse large amounts of reactants.
How do catalysts speed up reactions?
They decrease the activation energy needed for a reaction to occur.
What does a catalyst provide to lower activation energy?
An alternative reaction pathway that has a lower activation energy.
Why does a lower activation energy increase the rate of reaction?
More particles have at least the minimum amount of energy needed when they collide.
What does activation energy look like on a reaction profile?
It’s the difference between the energy of the reactants and the highest point on the curve.
How can you compare activation energy with and without a catalyst on a reaction profile?
The highest point on the curve is lower for the reaction with a catalyst.
In a reaction profile, what does the curve look like with a catalyst?
It has a lower peak than the curve without a catalyst.
How does a catalyst affect rate?
- Particles must collide with enough energy.
- Catalysts provide an alternative pathway.
- This pathway has lower activation energy.
- More collisions successful.
- Reaction speeds up
-Increased rate
What does the rate of reaction measure?
How quickly reactants are used up or products are formed.
What is the formula for the rate of reaction?
Rate = Amount of reactant used or product formed ÷ Time
Why is it usually easier to measure the rate of reaction by observing products rather than reactants?
Because products are often easier to detect or measure than reactants disappearing.
How does the precipitation method work? (investigate how temperature affects rate)
- Mix two clear solutions that form a precipitate.
- Time how long a mark takes to disappear through the cloudy mixture.
