Physical Changes
Is it possible to reverse a physical change?
Yes
Is it possible to reverse a chemcial change?
What does a chemcial equation represent?
The summary of a chemical reaction.
State the law of conservation of mass.
In a chemical reaction, mass is neither created nor destroyed.
H₂ + O₂ → H₂O
2H₂ + O₂ → 2H₂O
What is a physical change?
In a physical change, the substance still consists of the same particles but the substance looks different before and after the change.
What is a chemical change?
A chemical change occurs when new substances are formed as a result of the change.
What are the substances on the right side of a chemical equation called?
Products
If 10 g of hydrogen reacts with 80 g of oxygen, what mass of water is produced?
90g
Na + Cl₂ → NaCl
2Na + Cl₂ → 2NaCl
Give an example of a physical change.
Teacher approves
Give an example of a chemical change.
Teachers approval
What are the substances on the left side of a chemical equation called?
reactants
True or False: The mass of reactants always equals the mass of products in a chemical reaction.
True.
Fe + O₂ → Fe₂O₃
2Fe + 3O₂ → 2Fe₂O₃
What are some indicators of identifying physical changes?
Change in shape, change in state (solid, liquid or gas), mixing two substances together.
What are some indicators of a chemcial change?
Smell, change in colour, gas or solid being produced, seeing light or a change in temperature.
Write the word equation for the reaction of hydrogen with oxygen to form water.
Hydrogen + Oxygen → Water
Why does the mass of magnesium increase when it reacts with oxygen in air?
Because it has reacted with the mass from the air, resulting in a product that has increased in mass.
C₃H₈ + O₂ → CO₂ + H₂O
C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
Why is cutting paper into smaller pieces considered a physcial change?
Although the product has changed and the substance is a different form, it is still the same type of particles; it has not transformed into anything different.
Why is cooking an egg considered a chemical change and not a physcial change?
Change in colour, change in state (liquid to solid), smell released
Write the equation for the reaction of hydrogen with oxygen to form water using chemical formulae. (double points if balanced)
2H2 + O2 → 2H2O
Why does mass seem to “disappear” when something burns?
Because some of the products are gaseous, resulting in the other products that have been produced to have 'lost' mass.
Al + HCl → AlCl₃ + H₂
2Al + 6HCl → 2AlCl₃ + 3H₂