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Chemical Kinetics

Chemical Kinetics. - Reaction Rates -. Learning Goals. Nitroglycerine. Discovered in 1847, nitroglycerine is an extremely unstable liquid – a physical shake can cause it to explode

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Chemical Kinetics

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  1. Chemical Kinetics - Reaction Rates -

  2. Learning Goals

  3. Nitroglycerine • 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

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

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

  6. 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

  7. 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

  8. Chemical Kinetics • 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)

  9. Reaction Rate • 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”

  10. Introduction to Chemical Kinetics • List 3 ways to make a chemical reaction go faster • Think of the Alka Seltzer reaction – how can you increase the rate of this reaction? • Think of the Mg + HClreaction – how can you increase the rate of this reaction? • Think of methanol + O2 – how can you increase the rate of this reaction? • 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? • Are there any chemical reactions that we want to slow down? • How could you slow the browning of an apple?

  11. Describing reaction rates • 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 ∆t Complete the sample problems on page 360/361

  12. Graphing rates of reaction • 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?

  13. Determining Average Rate of Reaction • Use a secant to determine the average rate of reaction. • Complete the sample question on page 363.

  14. Determining Instantaneous Rate of Reaction • Use a tangent to determine the instantaneous rate of reaction. • Complete the sample question on page 363.

  15. Measuring Rates of reaction • What types of equipment can we use? • Reactions that produce a gas: • Reactions that involve ions: • Reactions that change colour

  16. Homework • 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

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