Chapter 4A - Collision Theory
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What do chemical reactions involve?
• atom rearrangement • reactant collisions • bonds within reactants must be broken requiring activation energy • atoms rejoin and form new bonds as products releasing energy
What is the collision theory?
Describes conditions required for chemical reactions to occur
What are successful collisions?
Collisions that allow products to be formed
What are the conditions for a chemical reaction to occur?
Particles must physically collide with: * Sufficient kinetic energy * Correct orientation for bonds to actually break
Why must reactant particles have sufficient energy?
Required to break bonds within reactant particles overcoming the activation energy barrier
Define Rate of Reaction
Rate of change of concentration of reactants and products over time
What does reaction rate depend on?
• Frequency of collisions • Proportion of collisions that involve energies > EA
What are the factors affecting reaction rate?
• Temperature • Surface Area • Concentration • Pressure
How does Temperature affect reaction rate?
As temperature increases, average kinetic energy of particles & reaction rate increase because * particles move faster, colliding more often * Greater proportion of collisions have energy > EA (most important)
How does Surface Area affect reaction rate?
• collisions occur b/w particles at the surface of solid and particles of the other reactant • A finely divided solid has greater SA, so more particles are exposed to surface • collisions occur more often, increasing reaction rate
How does concentration affect reaction rate?
• When concentration of solution increases, there are more reactant particles in a given volume • Collision frequency and successful collisions increases, increasing reaction rate
How does Pressure affect reaction rate?
• increasing pressure increases reactant particles in a given volume • collision frequency, and collision success increases, increasing reaction rate
Define Open System
• Any gas produced in a reaction is allowed to escape • Both matter/energy are exchanged b/w system and surroundings
Define Closed System
• Any gas produced in a reaction cannot escape as the reaction vessel is airtight • only energy (not matter) is exchanged with surroundings • allows for possibility of reverse reactions
What are the common reaction rate measuring techniques?
• Temperature Change • Change in mass • Precipitation formation/colour change • Volume of gas evolved • pH change
Method and Type Technique: Temperature Change
Use a thermometer to measure the temperature change over time for an open system Quantitative Measurement
Technique: Change in Mass
Use a balance to measure the change in mass (formation of solid or a gas in an open system) over time Quantitative Measurement
Technique: Precipitate Formation/ Colour Change
Visual observation of the production of a precipitate or colour change over time for a open system Qualitative Measurement
Technique: Volume of Gas Evolved
Use a gas syringe to measure the volume of gas produced in a closed system over time Quantitative measurement
Technique: pH change
Use an indicator or pH probe to measure the change in pH of a reaction mixture over time for an open system Quantitative/Qualitative