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?