Chemical Kinetics- Reaction Rates -

Learning Goals

Discovered in 1847, nitroglycerine is an extremely unstable liquid – a physical shake can cause it to explode

In 1867, Alfred Nobel discovered that mixing it with silica paste to form a solid makes it more stable – he invented dynamite

Nitroglycerine

When detonated, the nitroglycerine undergoes a rapid and highly exothermic decomposition reaction, released an enormous amount of energy in less than a second!

Nitroglycerine

Dynamite was used extensively in the building of Canada’s railroads; nitroglycerine in its pure form was also used for tunnel blasting

Nitroglycerine

Nitroglycerine is also used as a heart medication

Treatment of angina, chest pain associated with clogged arteries and decreased blood flow, which reduces oxygen supply to the heart

Nitroglycerine

As a heart medication does not explode, it undergoes a different chemical reaction, which releases small amounts of nitric oxide (NO(g))

Nitric oxide acts on the walls of the blood vessels to makes their diameter larger

This increases blood flow and relieves angina

Production of nitrous oxide gas occurs at the much slower rate, releasing far less energy, so not harmful

Nitroglycerine

Chemical kinetics is the branch of chemistry concerned with the rates of chemical reactions

A rate is a change in a measurable quantity over time

Different chemical reactions proceed from reactants to products at different rates (e.g. combustion of propane and oxidation of silver)

Chemical Kinetics

The reaction rate of a chemical reaction is the change in concentration of a reactant or product per unit time

How do we determine the reaction rate of a specific chemical reaction?

Read and summarize p. 365 “Measuring Reaction Rates”

Reaction Rate

1) List 3 ways to make a chemical reaction go faster2) Think of the Alka Seltzer reaction – how can you increase

the rate of this reaction?3) Think of the Mg + HCl reaction – how can you increase

the rate of this reaction?4) Think of methanol + O2 – how can you increase the rate

of this reaction?5) Cars can produce more power (and therefore more

speed) if they can combust the fuel faster – what can drivers/engineers do to increase the rate at which fuelburns?

6) Are there any chemical reactions that we want to slow down?

7) How could you slow the browning of an apple?

Introduction to Chemical Kinetics

How do we determine the rate at which a car travels?

Similarly, how can we determine the rate at which a chemical reaction occurs?

Let’s develop an equation:

Average rate of reaction = change in concentration elapsed time

r = ∆c ∆tComplete the sample problems on page 360/361

Describing reaction rates

This graph shows the concentrations of both reactants and products as time elapses.

What do we notice about the curves? Explain this? What measurement should be used for the concentration instead of number

of molecules?

Graphing rates of reaction

Use a secant to determine the average rate of reaction. Complete the sample question on page 363.

Determining Average Rate of Reaction

Use a tangent to determine the instantaneous rate of reaction.

Complete the sample question on page 363.

Determining Instantaneous Rate of Reaction

What types of equipment can we use?1) Reactions that produce a gas:2) Reactions that involve ions:3) Reactions that change colour

Measuring Rates of reaction

Assigned Questions◦ p. 361 Practice UC # 1, 2◦ pp. 364 – 365 Practice UC # 3, 4, 5, 6◦ Read and Summarize p. 365 “Measuring Reaction

Rates”◦ pp. 365 – 366 Practice UC # 7, 8, 9, 11◦ Section 6.1 Questions UC # 1, 2

Assignment – p. 401 Lab Exercise 6.1.1 – Determining a Rate of Reaction◦ Students to complete Prediction, Analysis,

Evaluation, Synthesis

Homework