10 Rate of Reaction

Learning Outcomes:

At the end of the chapter, students must understand that:

   -  Rate of change is a ratio of two quantities, of which one is usually time (s). For example, volume of gas evolved per second.

   - Rate of change is affected by concentration, pressure, particle size and temperature. (Not required: effect of concentration and pressure)

At the end of the chapter, students must be able to:

     - Describe the effects of particle size and temperature on the rate of change.
     -Explain the effects in terms of collisions between particles.

     - Interpret data obtained from experiments concerned with rate of change. This includes the interpretation of
    graphs and calculation.

      1. What is the speed/rate of reaction?

a. Speed of reaction =   volume of gas evolved

                                                time taken 

b. Speed of reaction =  mass of product produced or amount of a reactant remaining 

                                                                        time taken 

   

 2. Measuring speed of reaction 

a. Measuring the volume of gas evolved 

•Graph shows:

–The gradient is greatest at the start.

–The gradient decreases with time.

–The gradient becomes zero when the reaction has completed. 

b. Measuring the volume of gas evolved 

•Measuring the change in mass of the reaction mixture

Speed of graph is measured by the gradient of the graph. 

Examples of fast or slow reaction:

1. Gummy bear Experiment

2. Iodine Clock 

3. Corrosion of metals

Exercise: Plot the graph of Mass of Reactants remaining against time for these three examples on the same graph. Assuming the initial and final of the reactants of the three examples are the same.

3. Factors affecting speed of reaction - particle size 

•Most chemical reactions of solids with liquids or gases go faster when the solids are broken into smaller pieces.

•Small pieces of solids have a larger total surface area than a large piece of the same mass.

•Therefore, there is more surface area for the acid particles to react with at any one time, more collisions between the reacting particles can occur, leading to a faster reaction.

•The larger the surface area of a reactant, the faster the reaction.

4. Factors affecting speed of reaction - temperature

•The speed of a chemical reaction increases when temperature increases.

•To react, particles must collide at great speed with a lot of energy. 

•At a higher temperature, reactant particles move faster. There is an increase in the number of effective collisions between the reacting particles. A larger number of the particles will therefore have the minimum activation energy to react when they collide, resulting in a faster reaction.

•The speed of a reaction is approximately doubled for every 10˚C rise in temperature.

5. End of Lesson Quiz 

09 Test for Gases

01 Test for Carbon Dioxide Gas

Expected Observation: Effervescence observed. A colourless and odorless gas evolved produced white precipitate in limewater. (No writing of chalky or milky or white suspension!!!) 

02 Test for Ammonia Gas 

Expected Observation: Effervescence observed. A colourless and pungent gas evolved turn damp red litmus paper blue.

03 Test for Oxygen Gas 

Expected Observation: A colourless and odorless gas evolved relights a glowing splint.

04 Test for Hydrogen Gas 

Expected Observation: Effervescence observed. A colourless and odorless gas evolved extinguishes lighted splint with a 'pop' sound.

08 Writing Word Equations for Acid Reaction...

01 Chemical Properties of Acid 

a) Acids react with reactive metals to form salts and hydrogen gas. 

b) Acids react with metal carbonates to form salts, carbon dioxide and water. 

c) Acids react with bases to form salts and water. 

With the help of the given examples below, write down any five possible reactions given the list of substances that can occur given in the link provided here. Write down suitable word equations representing the reactions. 

02 Acids + Reactive Metal -> Salts + Hydrogen gas 

E.g. Sulfuric acid + Sodium -> Sodium sulfate* + Hydrogen gas

* Sulfate because it consists of atoms of sulfur and oxygen.

03 Acids + Metal Carbonate -> Salts + Carbon dioxide + Water 

E.g. Nitric acid + Potassium carbonate* -> Potassium nitrate + carbon dioxide + water

*carbonates consist of atoms of carbon and oxygen bonded together.

04 Acids + Bases/Alkalis -> Salts + Water : Type of Reaction: Neutralisation reaction 

E.g. Hydrochloric acid + Sodium hydroxide -> Sodium chloride + water

07 Differences in Chemical Properties between Acids and Bases

Instructions: Watch the videos below for the various reaction of acids and bases with other substances. You may recall some of the observations made during your practical lessons. Make relevant observations and write suitable equations to represent the reaction. Write your answers in the link provided here. 

A summary of basic knowledge of Acids, Bases and Indicators are included here. 

1. Acids + Reactive Metals (Group I, II or III,  Zinc or Iron etc) --> salt + hydrogen gas 

E.g. Reactions of various metals with hydrochloric acid

2. Acids + Metal Carbonates --> salt + water  + carbon dioxide gas 

E.g. Calcium carbonate with acid

 3. Acids + Base  --> Salt + water (a form of neutralisation reaction) 

E.g. Titration of hydrochloric acid with sodium hydroxide

4. Alkalis + Ammonium salts --> salt + ammonia gas + water 

E.g. ammonium chloride + sodium hydroxide  --> sodium chloride + ammonia gas + water

06 General Differences between Acids and Bases - Differences between Acids & Bases

01 Activity - Finding the General Differences between Acids & Bases

In this group activity, you will research as a group to find the differences between acids and bases. Do find out also about salts, alkali and carbonates as well to make connection between them.

You will present your research finding via a mind map through mindmeister. Log on to mindmeister and register via your facebook account or create a new account. The link is here.

A raw sample can be viewed here.

Please complete your mind map within the stipulated time and paste your link into this document here.

Some common names of Acid, Bases, Carbonates, Salts etc You must know:
(Take note of those highlighted in red)

Acids	Bases		Metal Carbonates	Metal hydrogen carbonates	Salts
	Alkalis (Soluble)	Insoluble Bases			Salts containing metal ions	Ammonium salts
Hydrochloric acid	sodium hydroxide	copper (II) oxide	sodium carbonate	sodium hydrogen carbonate	sodium chloride	ammonium chloride
sulfuric acid	potassium hydroxide	copper (II) hydroxide	magnesium carbonate	potassium hydrogen carbonate	potassium iodide	ammonium nitrate
nitric acid	ammonium hydroxide	aluminium oxide	calcium carbonate		lead (II) nitrate
phosphoric acid	lithium hydroxide	lead (II) oxide	copper (II) carbonate		copper (II) sulfate
citric acid	calcium hydroxide (slightly soluble)	zinc oxide	zinc carbonate		Copper (II) nitrate
tartaric acid		lead (II) hydroxide	lead (II) carbonate		calcium sulfate
ethanoic acid		magnesium oxide	ammonium carbonate		barium sulfate

Gases you must know:

Ammonia	Hydrogen	Oxygen	Chlorine
Nitrogen	Steam	Carbon dioxide	Carbon monoxide

05 Changes in Temperature of the Surrounding

01 Temperature Changes of Surrounding due to Energy Changes During Reaction 

Chemical Changes are accompanied by a change in energy. When energy is given off during the reaction, temperature of the surrounding increases. When energy is absorbed during the reaction, the temperature of the surrounding decreases. 

02 Interpreting Temperature-Time Graph of Surroundings during Reaction 

a) For Reaction involving absorption of energy into the system: 

Energy is taken into the system when reaction is taking place. The thermometer recording the temperature recorded shows the temperature of surrounding temperature. Since energy is taken into the system, the surrounding temperature decreases. However, after the completion of reaction, temperature increases as heat is now released from the system for the system to reach thermal equilibrium with the surrounding. The room temperature is 25 degree Celsius. 

Examples of Changes involving absorption of energy: Boiling, Melting, Sublimation, dissolving, decomposition etc... 

b) For Reaction involving release of energy into the system: 

Energy is released to the system when reaction is taking place. The thermometer recording the temperature recorded shows the temperature of surrounding temperature. Since energy is removed from the system, the surrounding temperature increases. However, after the completion of reaction, temperature decreases as heat is now taken into the system for the system to reach thermal equilibrium with the surrounding. The room temperature is 25 degree Celsius. 

Examples of Changes involving release of energy: Combustion, photosynthesis, freezing, condensation etc... 

04 Writing Word Equations for Chemical Reactions

01 Interpreting Word & Chemical Equations:

In the reaction of the combustion of carbon to form carbon dioxide:

Carbon + oxygen gas -> Carbon dioxide gas [Word Equation]

Carbon and oxygen gas are reactants. Carbon dioxide gas is the product.

C (s)     +   O2  (g) -> CO2  (g)  [Chemical Equation]

C and O are chemical symbols of carbon and oxygen element.
Oxygen is a diatomic molecule so it appears as O2 . 
(s) and (g) are called state symbols ; they represent the state of the substance during the reaction.

You will learn more about writing chemical equations later. Now, you just focus on writing word equations. 

02) How do we write the name of the compound formed? 

Referring to the notes of naming compounds : Click here for recap on naming compounds.

03) Word Equation of Combination 

a) Sodium + chlorine gas -> sodium chloride
b) iron + sulfur -> iron sulfide
c) magnesium + oxygen -> magnesium oxide

04) Word Equation of Combustion/Rusting 

a) Combustion of Fuels:
i) Methane gas + oxygen gas -> carbon dioxide gas + water

b) Rusting of Iron 
Iron + oxygen -> Iron (III) oxide

Note: iron (III) refers to the charge the iron has when forming a compound with oxygen. It means it has a charge of 3+. You will study the charges of each element when forming compound later on. You will only need to write this (I), (II)  or (III) etc for certain elements. 

05) Word Equation of Decomposition 

a) Copper (II) Carbonate -> Copper (II) oxide + carbon dioxide
b) Zinc nitrate -> zinc oxide + nitrogen dioxide + oxygen
c) Water -> hydrogen + oxygen (Electrolysis)

06) Word Equation of Precipitation 

a) lead (II) nitrate + potassium iodide -> potassium nitrate + lead (II) iodide (yellow precipitate) 
b) copper (II) nitrate + sodium hydroxide --> copper (II) hydroxide (blue precipitate) + sodium nitrate

07 Complete the Exercise in this link provided as a group.