Unit 3: Reaction Kinetics

1. Mr. Chapman Chemistry 30 Unit 3: Reaction Kinetics

2. Beginning Reaction Kinetics • Kinetics is the branch of chemistry that is concerned with the rate of change of a chemical reaction. • The rate of changeof a reaction simply refers to the speed at which a reaction occurs. • Before we can study this rate of change, we need to readdress the traditional physics definition of speed briefly.

3. Physics – A Brief Review • When we talk about the speed of an object, we talk about the rate at which DISTANCE changes over TIME. • Speed = distance time v = Δd t

4. 2 Types of Speed Can Be Determined from a Distance vs. Time Graph • Average Speed – this is the speed of an object over a given period of time. You are most familiar with this – it is the slope of the best-fit line of a graph. • Instantaneous Speed – this is the speed of an object at a single instant in time. The instantaneous speed of an object it slightly more difficult to determine. It is the slope of a curve at one instant in time.

5. Average Speed from a Graph Speed is calculated by determine the slope of the best-fit line. Notice that the line does not grow through all of the points on the graph.

6. Instantaneous Speed from a Graph Notice that the speed of this object is not constant. To determine its speed at ONE POINT IN TIME, we find the slope of the TANGENT LINE at that particular time.

7. What is a Tangent Line? • A tangent line is a line that only touches a curve at one place, or one particular point. • The instantaneous speed of an object can be useful when the object is not moving at a constant speed. • The tangent line allows us to calculate a slope at a point where the graph is curved, and that is why it is useful.