Topic 1 - Stoichiometry

Question 1

what’s the name of the phase change when solid -> Gas

Answer 1

sublimation

Question 2

what’s the name of the phase change when solid -> liquid

Answer 2

melting

Question 3

what’s the name of the phase change when Gas -> Solid

Answer 3

deposition

Question 4

what’s the name of the phase change when Liquid -> Gas

Answer 4

boiling evaporation

Question 5

what’s the name of the phase change when Liquid -> solid

Answer 5

freezing

Question 6

what’s the name of the phase change when gas -> liquid

Answer 6

condensation

Question 7

what are the state symbols for
solid
liquid
gas
aqueous

Answer 7

• (s)
• (l)
• (g)
• (aq)

Question 8

what is aqueous solutions

Answer 8

solutions formed by dissolving a solid in a liquid

Question 9

Physical change

Answer 9

a substance only changes from one phase to another, without forming new substance.
eg, H2O(s) -> H2O(l)

Question 10

chemical changes

Answer 10

result in formation os new chemical substance.
the atoms in the reactants are rearranged to from new product.

Question 11

facts about chemical changes refer to (Law of conservation of mass)

Answer 11

In a chemical reaction matter is not created or destroyed.
1, number of atoms R=P
2, atoms of reactant has been rearranged to form the product.

Question 12

what are the two groups of matter

Answer 12

1, Pure substances
- element and compounds
2, Mixtures
- homogeneous or heterogeneous

Question 13

definition of elements

Answer 13

Is a substance that cannot be broken down into a simpler substance by chemical means.
- all known elements can be found on the Periodic Table

Question 14

definition of molecules

Answer 14

Electrically neutral group of two or more atoms bonded together.
H2,Cl2,N2

Question 15

electrically neutral

Answer 15

An object that has a balance of protons and electrons.
Opposite=charged objects

Question 16

Definition of compound

Answer 16

Formed from two or more different elements chemically joined in a fixed ratio.
eg. H2O

Question 17

key fact of compounds

Answer 17

They have different properties from the element that they are made from.
eg. 2Na+Cl2->NaCl
chlorine poisons gas and reactive metal = table salt

Question 18

Definition of mixture

Answer 18

They contain more that on element and/or compound that are not chemically rounded together and so
- retain their individual properties.

Question 19

two types of Mixture

Answer 19

1, homogeneous mixture
- have a constant composition throughout.
- they are mixed together.
2, heterogeneous mixtures have visibly different substance or phase.
- does not mix

Question 20

what can you do when balancing a chemical equation

Answer 20

only change the number in front of the R and P – coefficients.
H2O -> 2 H2O

Question 21

% Atom economy (equation )

Answer 21

% Atom economy = molar mass of the desired P / molar mass of all reactants x 100.
100 - the %AE = wasted reactants

Question 22

what is the unit of mole

Answer 22

mol

Question 23

state 2 equations to calculate moles

Answer 23

1, mol = mass/molar mass (n=m/M)
2, mol = concentration x volume (n=cV)
V must be in dm^3

Question 24

definition of mole

Answer 24

it is the SI unit for amount of substance (n),
1 mol = 6.02 x10^23 elementary entities.

Question 25

the number of Cl molecules and Cl atoms in 1.00 mol of Cl gas, Cl2.

Answer 25

• 6.02 x 10^23 molecules of Cl2
• 6.02 x 10^23 2x6.02 x 10^23 = 1.2x10^24 Cl atoms

Question 26

state the definition of relative atomic mass (Ar)

Answer 26

is the weighted average mass of the naturally occurring isotopes of an element relative to 1/12 the mass of an atom of C-12.
- find on PT
- eg. H = 1.01

Question 27

definition of AMU

Answer 27

Atomic mass unite, which has a mass of 1.66 x 10^-27

Question 28

calculating relative atomic mass (Ar)

Answer 28

Ar = (relative abundance x mass of the isotope) +()+() / 100

Question 29

state the definition of relative molecular mass (Mr)

Answer 29

Is the weighted average mass of a molecule relative to 1/12 the mass of an atom of C-12.
- is the sum of the Ar of the atoms in the molecule.
- eg, H2O = 2x H (1.01)
1 xO (16)
16 + 2x1.01 = 18.02

Question 30

the unit of Molar mass

Answer 30

g mol^-1

Question 31

Molar mass definition (M)

Answer 31

Is the mass in grams of one mole of a substance.
- one mole of substance contain 6.02 x 10^23 particles.
- numerically = relative atomic mass.

Question 32

Molar mass for molecules

Answer 32

The the sum of all (number of the atoms in the molecule x its Ar) = Mr of the molecule = M

Question 33

converting between cm^3 and dm^3

Answer 33

10^-3

1cm^3 x 1dm^3/1000cm^3 = 0.001dm^3

Question 34

where and what is Molar ratio

Answer 34

the Coefficients in the balanced equation tells the mol of R and P

2A + 3B -> C + 2D

2 mol of A react with 3 mol of B to form C and 2 mol of D

• one reactant is limiting and one is excess.