Particle Theory and Reaction Rates: Comprehensive Study Notes

Class Dates and Titles:
- Friday 5 June 2026: Gwaith Dosbarth (Classwork) - "Particle theory and temperature."
- Wednesday 20 May 2026: Gwaith Dosbarth (Classwork) - "Particle theory and temperature…continued."
Primary Learning Objective (Nod y wers):
- To explain how temperature affects the rate of a reaction using particle theory.

Definition of Chemical Reactions:
- A chemical reaction is a change in which atoms are rearranged to create new substances.
- Characteristics: These changes are often irreversible or not easily reversed.
Core Components:
- Reactants: The starting substances in a chemical reaction.
- Products: The new substances formed as a result of the reaction.
The Law of Conservation of Mass:
- No atoms are created or destroyed in a chemical reaction.
- The total mass of the reactants is equal to the total mass of the products ( $\text{Total Mass}_{\text{reactants}} = \text{Total Mass}_{\text{products}}$ ).
Observable Changes in Reactions:
- Colour change.
- Temperature change.
- Gas production (often seen as bubbling or effervescence).
- Solid formation (precipitation).

States of Matter Descriptions:
- Solid: Particles are closely packed in a regular arrangement (lattice) and vibrate about fixed positions.
- Liquid: Particles are close together but in a random arrangement; they can move over one another.
- Gas: Particles are far apart and move rapidly and randomly in all directions.
Effect of Heat on Particles (Extension):
- As particles get warmer, they gain more kinetic energy.
- In solids, this results in increased vibration. In liquids and gases, this results in faster movement.
PhET Simulation Variables:
- Substances modeled: Neon, Argon, Oxygen, and Water ( $H_2O$ ).
- Variables adjusted: Heat, Cool, States (Solid, Liquid, Gas).
- Example temperature observed: $28\,K$ .

Collision Theory Requirements:
- For reactant particles to react, they must first collide with one another.
- $\text{Reactant} + \text{Reactant} \rightarrow \text{Product}$
The Role of Temperature in Collision Theory:
- Kinetic Energy: As temperature increases, particles gain more kinetic energy and move faster.
- Frequency of Collisions: Faster moving particles collide with each other more frequently.
- Successful Collisions: Increasing temperature means collisions have more energy, increasing the likelihood that they will be "successful" (leading to a reaction).
Definition of 'Rate':
- The rate of a reaction is the speed at which the reaction takes place.

Case Study: Magnesium and Hydrochloric Acid ( $HCl$ ):
- Reaction 1: Magnesium ribbon added to cold hydrochloric acid.
- Reaction 2: Magnesium ribbon added to warmed hydrochloric acid.
- Observation: The reaction in warmed acid happens faster due to the increased frequency and energy of collisions.
Case Study: Copper and Oxygen:
- Reaction: Copper + Oxygen ( $2Cu + O_2 \rightarrow 2CuO$ ).
- Identification: Copper and Oxygen are the reactants.
- Identification: Copper oxide is the product.
- Requirement for reaction: Particles of Copper and Oxygen must collide with sufficient energy.

Volume of Gas vs. Time Graphs:
- Graphs plotting the volume of gas produced ( $cm^3$ ) against time ( $s$ ).
- Gradient (Steepness): A steeper curve (e.g., experiment 'a') indicates a faster reaction rate compared to a shallower curve (e.g., experiment 'b').
- Plateau: When the graph levels off (becomes horizontal), the reaction has stopped because one or more reactants have been used up.
Concentration vs. Time Graphs:
- Reactant Curve: Starts high (e.g., $0.10\,mol/L$ ) and curves downwards as the reactant is consumed.
- Product Curve: Starts at zero and curves upwards as the product is formed.
Specific Data Analysis (Limestone and Hydrochloric Acid):
- Reaction uses $100\,cm^3$ of hydrochloric acid at room temperature.
- Maximum volume of $CO_2$ produced: $100\,cm^3$ .
- Data point extraction: After $20\,s$ , the volume produced according to the graph is approximately $60\,cm^3$ .
- Reaction completion time: The graph levels off at approximately $60\,s$ .
Specific Data Analysis (Magnesium and HCl - Hydrogen formation):
- Graph A represents a standard reaction.
- If the same mass of magnesium ribbon and the same concentration of acid are used but at a lower temperature, the reaction will follow a different curve (e.g., Graph B).
- Explanation: At a lower temperature, particles have less kinetic energy, leading to fewer successful collisions per second and a slower reaction rate.

Task 1: View and take notes on the video resource (https://www.youtube.com/watch?v=v2D2Tx0pgWA).
Task 2: Sketch reaction rate graphs and identify whether a curve shows product or reactant based on its slope (Product increases over time; Reactant decreases over time).
Task 3: Complete past paper questions regarding gas volume and temperature changes.
Plenary (Diweddglo): Identify three keywords/terms and provide their definitions (e.g., Rate, Collision Theory, Irreversible).