Physical and Chemical changes

Question 1

Physical changes

Answer 1

No new substance is formed
changing in shape, size, texture, smell, and color.
basic composition and chemical properties remain the same
usually reversible
may or may not be an evolution of heat.
a substance may disappear but can be recovered

Question 2

Water below 4 C

Answer 2

Expands on cooling and contracts on heating

Question 3

Dissolution of substances

Answer 3

in water is a physical change.
solid=evaporation
liquid=distillation(fractional and simple)
gases= heating

Question 4

crystallisation

Answer 4

the process of formation of pure crystals from its solution.
crystals are the purest form of solids and have a definite shape.

Question 5

Chemical changes

Answer 5

heat or light, sound may be given off or absorbed
a new substance, gas may be formed
new substance may have diff properties

Question 6

Chemical reaction

Answer 6

og substances reactants undergo a change to form new substance=products

Question 7

symbol and chemical equation

Answer 7

represents one atom of an element-> represents one molecule of a compound or element

Question 8

law of conservation of mass

Answer 8

this property is used to balance a chemical eqaution
matter can neither be created nor destroyed, total mass b4 and after remain the same(same no of atoms on both sides)

Question 9

Evolution of gas

Answer 9

reactants=liquid or in solution form.
the bubbling conforms evolution of gas (effervescence).
arrow pointing upwards

Question 10

Change of colors

Answer 10

color of product differ from reactant

Question 11

Formation of precipitate

Answer 11

the precipitate is a solid product that separates out from the solution during a chemical change.
arrow pointing downwards

Question 12

Evolution of energy

Answer 12

almost all reactions have energy change.
energy usually in the form of heat may be released or absorbed.
the reactions where heat is involved is known as exothermic reaction

Question 13

Absorption of heat

Answer 13

endothermic reaction-> -Heat on right or +Heat on left

Question 14

Change of state

Answer 14

g=gas, liquid=l, solid=s, aqueous=aq(smth containing water) are written near the symbols or formulae of the reactants and products

Question 15

Types of chemical reactions- Synthesis reaction

Answer 15

Two or more substances combined to a form a new substance
may require heat, light or electricity
burning magnesium
2Mg+O2->2MgO

Question 16

Decomposition reaction

Answer 16

A single compound being broken into two or more elements(simple substances)
mainly endothermic
sugar+heat=black mass of charcoal

Question 17

Displacement reaction

Answer 17

a more reactive element displaces a less reactive element
Reaction of iron with copper sulfate solution