Chapter 22-Particle Size and Speed of Reaction(Group 3A)

Chapter 22: Speed of Reaction: 

Chapter 22: Speed of Reaction Particle Size and Speed of Reaction

Involving real-life situation: 

Involving real-life situation Many chemical reactions involve solid reactants. Cooking food is an example. Why do we often chop up food into small pieces before cooking it? We shall find out through this chapter.

Answer: 

Answer To answer the previous question, again consider the reaction between marble chips and dilute hydrochloric acid. Two flasks are set up. One flask contains a large piece of marble (calcium carbonate) while the other has small pieces of marble. Everything else in the two experiments is the same to ensure a fair test. Bubbles of gas are produced more quickly in Experiment 1. This indicates that the reaction is faster when small pieces of marble are used.

Two graphs obtained if the gas is collected and the volume plotted against time.: 

Two graphs obtained if the gas is collected and the volume plotted against time. Volume of gas (cm3) Time (min) Small marble chips (large surface area) End of reaction End of reaction Large marble chip (small surface area)

Slide 5: 

The initial gradient of the graph for the reaction with smaller pieces of marble is steeper. Thus, the speed of reaction is greater when smaller pieces of marble are used. Reactants are used up faster when small pieces of solid are used. Most chemical reactions of solids with liquids or gases go faster when the solids are broken into smaller pieces.

An explanation: 

An explanation Reactions take place when particles collide Small pieces of solid have a larger total surface area than a large piece of the same mass

An explanation: 

An explanation More surface area for the acid particles to react with at any one time More collisions between the reacting particles can occur Leads to a faster reaction

An explanation: 

An explanation Larger surface area of reactant quickens the reaction Solids Powder reacts faster than large pieces of solids Liquids A fine spray reacts faster than liquid not in the form of spray

Applications (The larger the size of particles, the faster the reaction.): 

Applications (The larger the size of particles, the faster the reaction.) Here are some applications of it. Just like what we have learn earlier in the Haber process, Iron catalyst is added to increase the speed of reactions. In order to make it more effective, the iron catalyst are finely divided to provide a larger surface area for reaction. Therefore, the smaller the size of reactants, the faster the reaction will be.

Slide 10: 

Done by: Ting Yee, Sumaiyah , Mervin, Daryl, Faizal 3EA 06/08/2011