Chemical Reactions

Chemical Reactions

What we will learn about

• Components of a chemical reaction

• Law of Conservation of Mass (Balancing Equations)

• Synthesis reactions

• Decomposition reactions

• Word and formula equations

• Types of Reactions: synthesis, decomposition, combustion, neutralisation, precipitation, acid reactions

• Important chemical reactions in living systems

Things to remember...

Things to remember...
Indicators of a Chemical Change

• Formation of new substances

• Energy change (energy released or absorbed - exothermic vs endothermic)

• Changes in chemical bonds in a substance

• Colour change

• Gas production

• Precipitate formation (forming a solid)

• Change in temperature

• Odour Production

Components of a Chemical Equation

• Words + formula

• Reactants

• Products

• Coefficients

• Subscripts

• The arrow

• The states

Components of a Chemical Equation

• Words + formula

• Reactants

• Products

• Coefficients - how many of a particular compound - we can change this number when balancing

• Subscripts - how many of a particular atom - we can NEVR change this number

• The arrow

• The states

How do we represent chemical equations?

Law of Conservation of Mass

Law of Conservation of Mass

• Matter cannot be created or destroyed, it can only change form

• The same amount and types of atoms in the reactants as there are in the products

• Just rearranged!

This means we have to balance equations - balancing means making the same amount of atoms on each side

We can't change the subscripts, but we can change the coefficients!

If we changed the subscripts, we would change the identity of the compounds.

Multiple Choice

How many silver (Ag) atoms are reactants in this equation?

4Ag + 3O₂ → 2Ag₂O

• 4

• 2

• 3

• 0

Multiple Choice

What does the Law of Conservation of Mass state?

• Matter cannot be gained or lost in a chemical reaction.
• Matter can only be lost in a chemical reaction.
• Matter can only be gained in a chemical reaction.
• Matter can be gained and lost in a chemical reaction. 

Multiple Choice

Balance this equation:

2Li + Cl₂ -> LiCl

• 2Li + Cl₂ -> 4LiCl2

• 2Li + Cl₂ -> LiCl₂

• 2Li + Cl₂ -> 2LiCl

How do we predict the products of a reaction?

• There are a number of common reactions that follow a predictable pattern

• The predictable patterns depend on the reactants (what is going into the reaction)

Synthesis Reaction

Decomposition Reactions

• Often requires energy input (to make the reaction go ahead, or to make it go faster)

​

everages

Example: Predicting products in a reaction

• Determine the reactants

• Recognise common reactions

• Determine the new formulas

Common Reaction Types

• Synthesis

• Decomposition

• Combustion

• Neutralisation

• Acid/base

• Acid/carbonate

• Precipitation

Multiple Choice

Which type of reaction is:

2 H₃AsO₄ → As₂O₅ + 3 H₂O

• Synthesis
• Decomposition
• Single Displacement
• Combustion

​Combustion Reactions

​Combustion Reactions

• ​a hydrocarbon fuel reacts with oxygen and releases heat

• ​also known as 'burning'

• ​complete or incomplete

• ​general form = fuel + oxygen --> carbon dioxide + water

• ​just have to balance!

​Combustion Reactions

• ​Can be complete or incomplete

• ​Complete = produces carbon dioxide

• Incomplete = produces carbon monoxide and extra carbon (soot)

​Other Combustion Reactions

• ​Metal + Oxygen:

  • Will always give us a metal oxide

  • ​then just have to balance it

​Other Combustion Reactions

• ​Metal + Oxygen:

  • Will always give us a metal oxide

  • ​then just have to balance it

• Corrosion

  • ​a specific metal oxide reaction

  • ​when a metal is exposed to oxygen and/or water

  • ​changes the metal into a more stable form, with a protective 'layer' on top to prevent more exposure to the air

Multiple Choice

What is essential for a combustion reaction to begin?

• Carbon dioxide
• Fuel 
• Fuel, oxygen and heat
• Water and oxygen

Multiple Choice

This burning of methane resulted in the formation of soot

• methane + carbon monoxide --> oxygen + carbon + water

• methane + oxygen --> carbon dioxide + carbon + water

• methane + oxygen --> carbon monoxide + carbon + water

Multiple Choice

Without balancing the final equation, predict the products for the synthesis reaction: $$Mg\ +\ Br_2\ \rightarrow$$ ?

• $$MgBr$$  

• $$MgBr_2$$  

• $$Mg_2Br$$  

• $$Mg_2Br_2$$  

Multiple Choice

Choose the balanced chemical equation for the formation of iron oxide.

• 2Fe + O₂ → 2FeO₂
• Fe + O₂ → FeO₂
• 4Fe + 3O₂ → 2Fe₂O₃
• 4Fe + O₂ → 2FeO₂

​Neutralisation Reactions

• Acid + base

• Acid + carbonate

​Neutralisation Reactions - acid + base

​Neutralisation Reactions - acid + base

• ​​acid + base --> salt + water ​

• not always the case, but for now this is a good general equation ​since you know the products

• all you have to do is balance

​Neutralisation Reactions - acid + carbonate

​Neutralisation Reactions - acid + carbonate

• ​acid + carbonate --> salt + water + carbon dioxide

• ​again, a neutralisation

• ​heating carbonates always decomposes the carbonate into its metal oxide + carbon dioxide

  • ​metal carbonate + heat --> metal oxide + CO₂

Multiple Choice

What type of reaction is shown?

Acid + Base → Salt + Water

• Combustion

• Neutralization

• Physical

• Nuclear

Multiple Choice

Which products are formed when an acid reacts with a base?

• an alcohol and carbon dioxide

• an ester and water

• a soap and glycerine

• a salt and water

Multiple Choice

An acid reacts with a metal carbonate to produce 

• Salt, water and hydrogen gas
• Salt, water and carbon dioxide
• Limewater
• Salt and water 

Multiple Choice

Complete the following reaction:

HCl + Mg(OH)₂ -->

• MgCl₂ + H₂O

• Mg +H₂O

• MgCl₂ + H₂

• MgCl₂ + H₂O + CO₂

Multiple Choice

Complete the following reaction:

HNO₃ + Ca(OH)₂ -->

• Ca(NO₃)₂ + H₂O

• Ca +H₂O

• Ca(NO₃)₂ + H₂

• Ca(NO₃)₂ + H₂O + CO₂

Revision: Solutions and Solubility

• ​​solutions are where a solute is dissolved in a solvent

• ​soluble = are able to be dissolved

• ​insoluble = unable to be dissolved

​

​

​Precipitation reactions are where two solutions are mixed together, and form an insoluble solid

Precipitation Reactions

• ​aqueous solution + aqueous solution --> aqueous solution + insoluble solid

Precipitation Reactions

• ​aqueous solution + aqueous solution --> aqueous solution + insoluble solid

• ​all you have to do is swap around the reactants to make the products, taking note of the charge

• ​AB + CD --> AD + CB

Precipitation Reactions

• ​aqueous solution + aqueous solution --> aqueous solution + insoluble solid

• ​all you have to do is swap around the reactants to make the products, taking note of the charge

• ​AB + CD --> AD + CB

Precipitation Reactions - determining the precipitate

• ​use your data sheet!

• the precipitate = insoluble

Multiple Choice

In writing the chemical equation for a precipitation reaction, what abbreviation of the physical state must appear with one of the products?

• (s)

• (g)

• (l)

• (w)

Multiple Choice

Predict the product(s) of this reaction (Don't worry about balancing the equation)

Pb(NO₃)₂ + KI →

• PbK(s) + INO₃(aq)

• No Reaction

• PbI₂(s) + KNO₃(aq)

• PbI₂(aq) + KNO₃(s)

Multiple Choice

Predict the products of the following equation.

MgCl₂ + AgNO₃ ---->

• AgCl(s) + Mg(NO₃)₂(aq)

• No Reaction

• AgCl(aq) + Mg(NO₃)₂(s)

• AgCl(s) + MgNO₃(aq)

Multiple Choice

What would be the formula of the precipitate that forms when Pb(NO₃)₂ (aq) and K₂SO₄ (aq) are mixed?

• K(NO₃)₂

• PbSO₄

• PbK₂

• H₂O