Chemistry - Chemical Change

Question 1

What is the difference between a chemical change and a physical change

Answer 1

Chemical change - when a substance or substances react to create a new substance or substances
Physical change - occurs when a substance undergoes a state change

Question 2

What are the characteristics of chemical reactions

Answer 2

1. The production of new substances with their own characteristic properties (e.g. state, melting point, colour, and density).
2. Energy changes such as temperature change, light, or sound.
3. Changes in state – e.g. formation of a gas or a precipitate (solid).
4. Consistent with the law of conservation of mass – i.e. the mass of the reactants is equal to the mass of the products.

Question 3

What is the difference between endothermic and exothermic reactions

Answer 3

Exothermic - releases heat, surrounds increase in temp
Endothermic - absorbs heat, cools surrounding

Question 4

What are some signs of a chemical change

Answer 4

• Change in odour
• Change in colour
• Change in energy (temperature, light)
• Formation of a precipitate (solid)
• Formation of a gas (bubbles)

Question 5

what is hydrocarbon combustion

Answer 5

substance containing hydrogen and carbon reacts with oxygen to produce carbon dioxide and water
(CxHx + O2(g) → CO2(g) +H2O(g)).

Question 6

What is a mol

Answer 6

• a quantity that chemists use to measure amounts of elements and compounds.
• The number of entities (atoms, molecules, formula units, or ions) in 1 mole is called Avogadro’s number (NA).
• Avogadro’s number = 6.02 x 1023 or 602 000 000
  000 000 000 000 000.

Question 7

what is the atomic molar mass vs the molar mass

Answer 7

Atomic molar mass - mass one mole of a particular element – found on the periodic table.
Molar mass - the mass in grams of 1 mol of a substance – measured in grams/mol.
- Determined using the chemical formula of the
substance and the atomic molar mass values from
the periodic table.