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Science

Fundamental chemical concepts

Formulas and equations

You should recall certain chemical formulas. You should also be able to write balanced symbol equations if you are given the formulas of the reactants and products.

Specified formulas- both tiers

Formulas of substances

nameformula
oxygenO2
carbon monoxideCO
carbon dioxideCO2
waterH2O
calcium oxideCaO
calcium carbonateCaCO3
hydrochloric acidHCl
sodium chlorideNaCl
potassium chlorideKCl
nitrogenN2
ammoniaNH3

Balancing equations

Example: write the balanced equation for the reaction between hydrogen and oxygen to produce water.

Step 1

Write the formulae for each substance:

H2 + O2 → H2O

Step 2

Check for an unbalanced element, for example, O. Adjust the number of each atom or molecule needed, but never change a formula. We need two O atoms on each side:

H2 + O2 → 2H2O

Step 3

Check for another unbalanced element. In this example, there are 2 H atoms on the left and 2 × 2 = 4 atoms on the right. So we need to double the number of hydrogen molecules:

2H2 + O2 → 2H2O

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