Physical change... Flashcards
Physical Property:
property of a substance identified without a change in composition
Ex. Density, viscosity, colour, lustre
Chemical Property:
property identified by its composition through a chemical change
Ex. Reactivity with acid, combustibility, light sensitivity
Physical Change:
does not alter chemical composition
- Examples: Crushing a can, Melting ice cube, Boiling water, Breaking a glass, Shredding
paper, Chopping wood.
Chemical Change
chemical structure is altered; the original substance is transformed through a rearrangement of atoms
- Examples: Cooking an egg, Heating sugar to form caramel, Baking a cake, Rusting of
iron.
Signs of Chemical Change:
Signs:
●Color Change
●2. Production of an odor
●3. Change of Temperature
●4. Evolution of a gas (formation of bubbles)
●5. Precipitate (formation of a solid)
●6. Original substance is used up
How energy relates to physical and chemical changes
Physical and chemical changes are usually accompanied by changes in energy
For example, when you sweat, water evaporates off the surface of your skin absorbing energy. This makes your skin feel cold
The total energy of an object is a sum of the kinetic energy and potential energy
Kinetic energy
energy associated with matter in motion
Proportional to its velocity
Potential Energy
energy associated with position/ composition (bond energies)
Increase height, increase potential energy
Thermal Energy
energy associated with the temperature of an object
Due to the motion of individual atoms
Law of energy:
Energy cannot be created or destroyed
Energy can be converted into different forms
Even though the energy changes form, there is no energy loss
percentage error:
% error = ⏐observed value – predicted value⏐ x 100%
predicted value
How to write numbers
Digits are grouped in three using a space instead of commas; e.g. 1 674.14.
Leave a space between the last digit and the SI unit: e.g. 12.5 m
Do not use a period after the SI unit.
Units are not pluralized.
Use product dots between different SI units; e.g. kPa·L/mol·K
Do not mix words & symbols; meter/s should be m/s or meter per second
Use symbols instead of full names for units, with numerals; e.g. 458 cm
Use prefixes so that numerals lie between 0.1 and 1000; e.g. 55 000 g should be 55 kg
Sig Fig rules
All nonzero digits are significant. 28.03 0.0540
Interior zeros are significant. 408 7.0301
Leading zeros are not significant. 0.0032 0.00006
Trailing zeros are sometimes significant:
after a decimal point are significant 45.000 3.5600
before a decimal point are significant 140.00 2500.55
before an implied decimal point are ambiguous and scientific notation should be used.
