Rates & Reactions (9th grade)
We can get an idea of how fast a chemical reaction is happening by observing how active it looks. One easy way is by watching the number of bubbles produced during the reaction. If you see a lot of bubbles quickly, it suggests the reaction is fast and vigorous. On the other hand, if there are only a few bubbles, the reaction is slower and less intense.
But to truly compare the speed of different reactions, we need more than just observations we need actual measurements. In the next section, we'll learn how to calculate reaction rates using numbers and data.
🔬 1. What is Rate of Reaction?
The rate of reaction tells us how fast a chemical reaction takes place. It answers the question: How quickly are the reactants turning into products?
Formula:
Rate = Mass of Reactants Used ÷ Time
You can also use:
Rate = Volume of Gas Produced ÷ Time (for reactions producing gas)
Example:
If 2g of magnesium reacts completely in 10 seconds:
Rate = 2g ÷ 10s = 0.2 g/s
📚 2. Important Vocabulary
Reactivity Series: A list that shows how reactive metals are. For example, potassium is more reactive than iron.
Displacement Reaction: A more reactive element kicks out a less reactive one from a compound.
Concentration: More particles in a space = more collisions = faster reaction.
Catalyst: A helper chemical that speeds up the reaction but is not used up.
🧪 3. Collision Theory
What it means:
Chemical reactions happen when particles (atoms or molecules) collide with enough energy. If the particles don’t collide hard enough, no reaction happens.
Real-life example:
Lighting a gas stove the gas (fuel) must mix with oxygen and receive a spark (activation energy) to ignite.
Using the Simulation:
Go to the “Single Collision” or “Many Collisions” tabs. Press "Play" and watch how particles bounce around and react. Try adjusting the energy levels using the sliders. See what happens when particles have low vs. high energy.
👉 Watch how more energy = more successful reactions.
💧 4. Concentration Effects
When you increase concentration:
You add more particles to the same space.
This means more collisions.
That leads to a faster reaction.
Concentration refers to how much of a substance is present in a space. A higher concentration means more particles are available to collide leading to faster reactions.
Real-life example:
Bleach cleans faster when it’s undiluted because the concentration of active particles is higher.
Using the Simulation:
Under “Many Collisions”, increase the number of reactant particles (A and B) using the particle counters.
👉 You’ll see more frequent collisions and faster reactions when more particles are present.
🔥 5. Temperature Effects
When you raise the temperature:
Particles move faster (more kinetic energy).
Collisions happen more often and with more energy.
This increases reaction rate.
Higher temperature makes particles move faster. Fast-moving particles collide more often and with more energy, increasing the reaction rate.
Real-life example:
Food cooks faster in hot water than cold water because heat speeds up chemical reactions.
Using the Simulation:
Use the temperature slider to raise the temperature in the simulation.
👉 Notice how the particles speed up and more reactions happen in less time.
🔁 6. Reversible Reactions & Equilibrium
Some reactions can go forward and backward they don’t just stop once products are made. This is called dynamic equilibrium.
Real-life example:
Carbon dioxide and water in soda can change back and forth that’s why soda goes flat!
Using the Simulation:
Switch to the “Reversible Reactions” tab. You’ll see the products forming and breaking down again.
👉 Try changing the amount of reactants or products to see how the reaction balances over time.
⚙️ 7. Catalysts
A catalyst is something that helps a reaction go faster without being used up.
Real-life example:
Your car has a catalytic converter to help reduce pollution by speeding up chemical reactions that break down harmful gases.
Using the Simulation:
Look for the “Add Catalyst” option (in the reversible or many collisions tabs).
👉 Turn it on and compare how long the reaction takes with and without the catalyst. You'll see the reaction speeds up but the catalyst remains
🔁 8. Displacement Reactions (Link to Reactivity Series)
A displacement reaction happens when a more reactive element pushes out a less reactive one from its compound.
Real-life example:
Zinc displacing copper from a solution of copper sulfate.
Zn + CuSO₄ → ZnSO₄ + Cu
Zinc displaces copper because it’s more reactive.
Using the Simulation:
While the PhET simulation doesn’t directly show displacement, you can connect the speed and reactivity.
📊 How to Use the Graph
What it means:
Graphs help us see how fast the reactants are used or products formed over time.
Using the Simulation:
After starting a reaction in the “Many Collisions” or “Reversible Reactions” tab, click “Graphs” to view data in real-time.
👉 Use this to compare how changing variables like temperature or concentration affects the reaction speed.
🌍 Real-Life Examples:
Cooking: Fast reactions when frying, slow ones when marinating or baking.
Rusting: A slow chemical reaction with oxygen and water.
Fireworks: Very fast chemical reactions releasing gases and light.
Let me know if you'd like these turned into slide format or interactive quiz questions!
