Chemical Equations

Chemical Equations

Multiple Choice

How many squares are there?

• 24

• 28

• 36

• 40

• 42

Multiple Choice

If I split water into its elements, what will I get?

• Hydrogen and Carbon

• Hydrogen and Oxygen

• Oxygen and Nitrogen

• Just more water

A Hofmann voltameter is a piece of lab equipment used to split water into hydrogen and oxygen using electricity.

When an electric current passes through the water (with a bit of acid added to make it conduct), it breaks down into hydrogen and oxygen.

Splitting Water

• Why do you think one side has twice as much gas as the other?

• ​How can we tell which is which?

What do you see?

Splitting water with the voltameter proves the LAW OF CONSERVATION OF MASS because the same atoms are still present, just rearranged into hydrogen and oxygen.

We see twice as much hydrogen as oxygen because water has two hydrogens for every one oxygen.

In today’s lesson, we are going to learn how to write word equations and then turn them into symbol equations. The equations for splitting water are:

​Word:
Symbol:

​water → hydrogen + oxygen
2H₂O → 2H₂ + O₂

​Word equations show the names of substances and are good for learning reactions. Symbol equations show the formulas of substances, including how many atoms of each element are involved. They're easier for calculations.

Multiple Choice

The blue atoms are called 

• metals
• nonmetals
• metalloids
• noble gases

Multiple Choice

The yellow atoms are called 

• metals
• nonmetals
• metalloids
• noble gases

Multiple Choice

Which of the following is a compound?

• Co
• O₂
• C
• CO₂

Word Equations

Word equations rules...

• Reactants always go first in word equations

• The products are written after the arrow

• Always write the names of the chemicals - not their symbols or formulas.

• Example: zinc + hydrochloric acid → zinc chloride + hydrogen

Multiple Choice

In the chemical equation below, what is the PRODUCT?

NaCl → Na + Cl

• Na + Cl

• NaCl

• →

• N

Multiple Choice

In the chemical equation below, what is the REACTANT?

CO₂ → C + O₂

• →

• C + O₂

• CO₂

• physical change

Write the word equation for:

When calcium chloride and potassium phosphate are dissolved in water

they react to form aqueous potassium chloride and calcium phosphate

powder.

Write the word equation for:

When calcium chloride and potassium phosphate are dissolved in water

they react to form aqueous potassium chloride and calcium phosphate

powder.

calcium chloride + potassium phosphate → potassium chloride + calcium phosphate

Write the word equation for:

When dissolved barium chloride reacts with dissolved potassium sulfate in water, barium sulfate solid and dissolved potassium chloride are made.

Write the word equation for:

When dissolved barium chloride reacts with dissolved potassium sulfate in water, barium sulfate solid and dissolved potassium chloride are made.

​barium chloride + potassium sulfate → barium sulfate + potassium chloride

Multiple Choice

Sodium reacts with chlorine to produce sodium chloride. Choose the correct word equation.

• sodium chloride → chlorine + sodium

• sodium + carbon dioxide → sodium carbonate

• sodium + chlorine → sodium chloride

Multiple Choice

Magnesium reacts with oxygen to form magnesium oxide. The correct word equation is...

• A

• B

• C

• D

Symbol Equations

​Unbalanced

​Metals lose electrons, non-metals gain, the charges balance to equal 0.

Use the criss-cross method: swap the charges as subscripts.

(e.g. Ca²⁺ + Cl⁻ → CaCl₂).

Ionic Compounds

​Atoms share electrons, no charges to balance,

Use prefixes in the name to tell the number of atoms (mono, di, tri, etc.).

(e.g. CO₂ = carbon dioxide, N₂O₄ = dinitrogen tetroxide).

​​Covalent Compounds

Multiple Choice

What is the correct formula for Lithium Oxide?

• LiO

• LiO₂

• Li₂O

• Li₂O₂

Multiple Choice

How many elements are in C₆H₁₂O₆?

• 1
• 2
• 3
• 24

Multiple Choice

Which is the correct formula for this compound?

Grey = Carbon, White = Hydrogen, Red = Oxygen

• C₇H₃OH

• C₈H₃O

• C₃H₈O

Multiple Choice

Magnesium reacts with oxygen to make magnesium oxide.
Which equation shows the correct product?

• Mg + O₂ → MgO

• Mg₂ + O₂ → MgO₂

• Mg + O₂ → Mg₂O

Multiple Choice

Aluminium reacts with oxygen to make aluminium oxide.
Which equation shows the correct product?

• Al + O → AlO

• Al + O₂ → Al₂O₃

• Al₂ + O₂ → Al₂O

Multiple Choice

Which is the correct chemical equation for the following: Barium Chloride combined with sodium sulfide → barium sulfide and sodium chloride

• BaCl + NaS → BaS+ NaCl

• BaCl₂ + Na₂S → BaS+ NaCl

• BaS+ NaCl → BaCl + NaS

• BaCl₂ + Na₂S → BaS+ NaCl₂

Another video for more examples and polyatomic ions...