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

Components of a Chemical Reaction

• Words + formula

• Reactants

• Products

• Coefficients

• Subscripts

• The arrow

• The states

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

Law of Conservation of Mass

Law of Conservation of Mass

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

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

• Different compounds, but the same 'stuff', just rearranged

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)

Example: Predicting products in a reaction

• Determine the reactants

• Recognise common reactions

• Determine the new formulas

Common Reactions

• Synthesis

• Decomposition

• Combustion

• Precipitation

• Acid/base

• Acid/carbonate

Multiple Choice

Which type of reaction is:

2 H₃AsO₄ → As₂O₅ + 3 H₂O

• Synthesis
• Decomposition
• Single Displacement
• Combustion

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