1. Chemical Equations and Reactions
Describing Chemical Reactions

2. Describing Chemical Reactions
What are some signs that a chemical reaction is occurring?

3. Indications of a Chemical Reaction
In a chemical reaction, one or more substances are changed into one or more NEW substances.
Indications of a chemical reaction include signs that a new substance has formed.

4. Indications of a Chemical Reaction
1. Evolution of heat and/or light

5. Indications of a Chemical Reaction
2. Production of a gas
Vinegar + baking soda

6. Indications of a Chemical Reaction
3. Formation of a precipitate
(NH4)2S(aq) + Cd(NO3)2 (aq)

7. Indications of a Chemical Reaction
4. Color Change
Phenolphthalein + NaOH

11. Writing Chemical Equations
Solid sodium oxide is added to water at room temperature and forms sodium hydroxide (dissolved in water). Write the word equation: Sodium oxide + water  sodium hydroxide Write the formula equation: Na2O(s) + H2O(l)  2 NaOH(aq)

12. Write formula equations for each of the following chemical reactions.
Hydrogen peroxide in an aqueous solution decomposes to produce oxygen and water.
Solid copper metal reacts with aqueous silver nitrate to produce solid silver metal and aqueous copper (II) nitrate.
Solid zinc metal reacts with aqueous copper (II) sulfate to produce copper metal and aqueous zinc sulfate.

13. Translating Chemical Equations
PbCl2 (aq) + Na2CrO4 (aq)  PbCrO4 (aq) + 2 NaCl(aq) Write a sentence explaining the above reaction: Aqueous solutions of lead (II) chloride and sodium chromate react to form a precipitate of lead(II) chromate and aqueous sodium chloride.

14. Translate the following into sentences:
2 ZnO(s) + C(s)  2 Zn(s) + CO2 (g)
Na2O(s) + 2 CO2 (g) + H2O(g)  2 NaHCO3 (s)

15. Write and balance equations for each of the following reactions:
Calcium metal reacts with water to form aqueous calcium hydroxide and hydrogen gas.
Nitrogen dioxide gas reacts with water to form nitric acid and nitrogen monoxide gas.
Potassium chlorate decomposes to form potassium chloride and oxygen.

16. Synthesis
Iron corrodes in the presence of oxygen forming iron (III) oxide.
Ammonia is formed by the combination of nitrogen and hydrogen at high temperatures and pressure.

17. Decomposition
The electrolysis of water results in the formation of hydrogen and oxygen.
When heated, sodium bicarbonate decomposes to sodium carbonate, water, and carbon dioxide.

18. Single Replacement
The addition of hydrochloric acid to magnesium results in the formation of hydrogen gas and magnesium chloride.
Sodium reacts violently with water, resulting in the formation of sodium hydroxide and hydrogen gas.

19. Double Replacement
When aqueous solutions of potassium iodide and lead (II) nitrate are mixed, a solid precipitate forms: lead (II) iodide.
Hydrochloric acid is neutralized by addition of a base (sodium hydroxide) resulting in the formation of water and a salt.

20. Combustion
Ethanol (C2H5OH) burns in oxygen, producing carbon dioxide and water.
Welders use acetylene (C2H2) torches. The flame is produced as acetylene burns in the presence of oxygen.

22. Using the Activity Series
Zn(s) + H2O(l)  no reaction Sn + O2  SnO2 Cd + Pb(NO3)2  Cd(NO3)2 + Pb Cu + HCl  no reaction

23. Will the following reactions occur?
MgCl2 (aq) + Zn(s) Al(s) + H2O(g)  Cd(s) + O2 (g)  I2 (s) + KF 