NOTES: Chemical Changes sec2
formulas
acid + metal ---> salt + hydrogen gas
acid + carbonate ---> salt + carbon dioxide + water
acid + alkali ---> salt + water
note:
- all combustion reactions are oxidation reactions but not all oxidation reactions are combustion reactions
@@Experiments@@
check for hydrogen gas:
turn on a Bunsen burner and light a splint, place lighted splint into the mouth of the test tube if light extinguishes and pop sound is heard hydrogen is present
note: light extinguish but no pop sound. hydrogen not present.
check for carbon dioxide:
bubble the gas into test tube containing limewater, if white precipitate is seen in limewater carbon dioxide is present
%%Physical and Chemical changes table%%
| Physical changes | Chemical changes |
|---|---|
| no new substances formed | one or more new substances formed |
| changes can be easily reversed using separation methods | changes cannot be easily reversed using separation methods |
| absorption and release of energy usually not involved | absorption and release of energy usually involved |
| break up ---> physical process | break down ---> chemical process |
%%Chemical changes%%
types of chemical changes:
Combined together ---> two or more substances combined together to form one or more new substances
Break down ---> a substance breaks down into two or more simpler substances
when they occur:
Are mixed:
- acid + metals
- acid + carbonate
- acid + alkali
Are heated:
- combustion of substances
- thermal decomposition of metal carbonates
Are exposed to light:
- photosynthesis
- light decomposition of silver chloride
Interact with oxygen:
- respiration
- oxidation
Interact with an electric current:
- electrolysis (electroplating) (coating a metal with another metal using electricity
%%Word equations%%
reactants ---> written on the left side of arrow
products ---> written on right side of arrow
conditions ---> middle of arrow
metal always first
exp: magnesium + oxygen --(heat)--> magnesium oxide
%%Atoms during a chemical reaction%%
- atoms not created or destroyed only rearranged
- mass is conserved during a chemical change (number of atoms stay the same so mass stays the same)
- old bonds in reactants are broken
- atoms rearrange themselves
- new bonds are formed in products
==Types of Chemical Changes==
- %%Oxidation%%
- ==Thermal decomposition==
- @@Neutralisation@@
%%1. Oxidation%%
occurs: the addition of oxygen to a substance
example:
rusting of iron nails
iron + oxygen + water ---> iron oxide (rust)
occurs: a substance is heated in the presence of oxygen. heat and light is usually given out
heat must be given out
==3. Thermal decomposition==
occurs: when substance breaks down into two or more simpler substances when heated
@@4. Neutralisation@@
occurs: when acid mixes with alkali
==Acids:==
- hydrochloric acid
- citric acid
^^Alkali:^^
- ammonia
- bleach
- potassium
%%pH levels%%
- solutions with a pH value less than 7 are acidic (0-6)
- solutions with a pH value more than 7 are alkali (8-14)
- solutions with a pH value of 7 are neutral (7)
universal indicator is used to provide a specific colour for each pH