Chemical Equations

11/24/14

Chemical equations

• Starting materials called reactants are shown on the left of the arrow

• Ending materials called products are shown on right of the arrow

NaCl + KOH NaOH + KCl

Diatomic elements

• Some elements always come as a pair of atoms when in element form

• H2, N2, O2, F2, Cl2, Br2, I2

• Other elements sometimes come in unique amounts such as S8 and P4

Subscripts vs. Coefficients

• Subscripts are used to make stable compounds. They show how the elements bond with each other.– H2O and H2O2

• Coefficients tell how many of the compound are involved in the reaction.

• 2 H2O

Chemical equation symbols

• yields• reversible reaction • heat Δ reactants are heated• Pressure pressure exceeding atmospheric

pressure is used• Catalyst a catalyst is used to speed up the rate of

reaction

Compounds

• If the name uses prefixes it is a covalent compound. Determine subscripts using prefixes

• If the name does not use prefixes it is an ionic compound. Look up charges and criss cross to find subscripts

Compounds

• If the name of the compound doesn’t end in –ide, it includes a polyatomic ion. Put it in parenthesis and then criss cross charges.

• Sulfate= SO4-2

• Hydroxide= OH-1

Compounds

• with special names:– Ammonia= NH3

– Hydrogen peroxide= H2O2

• Acids:– Sulfuric= H2SO4

– Hydrochloric=HCl– Nitric= HNO3

States of matter symbols

• (s) solid• (l) liquid• (g) gas• (aq) aqueous; dissolved in water• solid, precipitate product• gaseous product