Identifying PHYSICAL and CHEMICAL CHANGES?

Question

Please identify wether it is a physical or a chemical change and specify if itis an exothermic or endothermic change..
Explain if necessary.

1.When a grain of table salt is placed in a 5mL of 0.1M silver nitrate solution.
2. A 0.5g of table salt in 5mL of water in a test tube.
3 Evaporation of acetone in a watch glass.
4.Combustion of acetone.
5. Strongly heated sugar.
6. Heated few grains of clean sand.
7. Aluminum dissolved in the acid and gave off Hydrogen gas.
8. Ammonium chloride dissolved in water and evaporated to dryness.

Thankyou very much!

Answer 1

1. Chemical
2. Physical
3. Chemical
4. Chemical
5. Chemical
6. Physical (Assuming nothing burned)
7. Chemical
8. Chemical

All you have to do to know the difference is that it's chemical if the actual chemical make-up of the material changes. If it's just a color change or a phase change or something dissolving (like salt and water) then it is a physical change.

Answer 2

From http://antoine.frostburg.edu/chem/senese/101/reactions/glossary.shtml

physical change: A change which does not transform one substance into another. For example, freezing water is a physical change because both water and ice are H2O. However, electrolysis* of water would not be a physical change because passing a strong electric current through water can decompose it into H2 and O2.

chemical change: A chemical change is a dissociation, recombination, or rearrangement of atoms.


1. NaCl + AgNO3--> NaCl ionizes (dissociates), thus chemical
exothermic since chlorides release E upon ionization

2. chemical and exo- (see above)
3. state change only, thius physical; endothermic since evaporation requires E from environment
4. combustion = burning, thus products are carbon dioxide and water (chemical); exo- since heat is released
5. sugar has fairly high melting point, so this could be a combustion rxn. (see 4 above)
6. no change to sand...no change to water; heat in = endo-
7. gas product is your key to chemical; exo- since metal dissolved
8. chemical (dissolving, ie ionizing), then physical (evaporation);
exo- for both

Answer 3

Chemical substitute: a million. colour substitute 2. ***capability substitute--->warmer of chillier 3. Precipitates---> reliable formed from ideas 4. Emitted gas actual substitute: a million. length 2. shape 3. section

Answer 4

1.chemical
2.chemical
3.physical
4.chemical
5.physical
6.physical
7.chemical
8.physical