reaction rates & collision theory chemistry. what is a rate? what does a rate involve? in...
TRANSCRIPT
REACTION RATES & COLLISION THEORY
Chemistry
What is a rate?
What does a rate involve?
In science, rate describes…
A Savings Rate
CO2 Concentration Increase Rate
Heart Rate
Rates in Science
Rates in Science: Change in “something” PER TIME (divided by) ALWAYS PER TIME!!! TIME: s, min, hr, day, yr
Examples: Moving Rate: mi/hr Your Growth Rate:
in/yr lb/yr lb/wk
Rates in Chemistry
Reaction Rate- Change in the amount of reactant or product per unit time.
More Rates in Chemistry
Rates can be measured by: Change in Reactant per time Change in Product per time
Reaction Rates ARE NOT constant throughout the reaction
Rate of Reaction from A Graph Rate at any time:
Slope of the Tangent Line
This graph shows the rate of reaction after about 50 seconds
Collision Theory – To Explain Reaction Rates
In order to react:
1. Molecules/Atoms must collide to react
2. Must collide in the correct place
3. Must have enough energy when they collide
Geometry (orientation) of Collision Molecules have to
collide with the correct geometry (orientation) to react
On the right, only the first type of collision will react for this particular reaction
Energy Diagrams & Transition States
Transition state: “Middle Product” Occurs when
reactants have enough energy
Ea (Activation Energy) Energy barrier for the
forward reaction
Energy of Collision
Reactants must overcome the Ea to react!
•Is this reaction endothermic or exothermic?
•What would the graph for the other type of reaction look like?
Energy Diagram Questions
1. Is this reaction exothermic or endothermic?
2. The energy change for this reaction is 50 kJ and the Ea for the forward reaction is 120 kJ. What is Ea for the reverse reaction?