2.1. Chemical equations and reactions

Question 1

the law of conservation of matter

Answer 1

because the same atoms are present in a reaction at the beginning (reactants) and at the end (products), the amount of matter in the system does not change - this is why chemical equations must be balanced

Question 2

reactants
products

Answer 2

• the substances that exist before a chemical reaction takes place
• the new substances that are formed during the chemical changes

Question 3

types of phases in chemical equations

Answer 3

solid (s), liquid (l), and gaseous (g) phase

Question 4

alternative symbol used to indicate a precipitate in chemical equation

Answer 4

arrow pointing down (alternative to (s))

Question 5

alternative symbol used to indicate a gaseous product

Answer 5

arrow pointing up (alternative to (g))

Question 6

above the reaction arrow can be written:

Answer 6

• pressure (and its exact amount)
• temp. at which react. was carried out
• “delta” meaning that the reactants were heated
• name of a substance that serves as the catalyst in the reaction

Question 7

types of chemical reactions

Answer 7

• synthesis (combination) - simple to complex
• decomposition - complex to simple
• single replacement reaction (AB + C -> A + BC)
• double replacement reaction (AB + CD -> AC + BD)
• neutralization reaction (acid + base -> salt + water)
• combustion reaction - a hydrocarbon reacting with oxygen
• polymerization (monomer + monomer = polymer)

Question 8

relative atomic mass (Aˇr) =

Answer 8

actual mass/u (u=1/12 actual mass of C-12=1.66*10^-27 kg)

Question 9

1. n=

Answer 9

m/M [mol=g/gmol^-1)

Question 10

2. n=

Answer 10

N/NˇA (N = number of particles, Nˇ = Avogadro’s constant = 6.022*10^23 mol^-1)

Question 11

In calculations with a limiting reactant, to find the number of moles of a product of interest, its stoichiometric coefficient and no of moles has to be put in the ratio/compared with…

Answer 11

…the stoichiometric coefficient and the number of moles of the limiting reactant

Question 12

To identify the limiting reactant we have to…

Answer 12

…compare the no of moles with stoichiometric coefficients of the reactants and evaluate which reactant is present in excess and which is not (limited).

Question 13

C =

Answer 13

n/V [M=mol/L]

Question 14

mass concentration (of solvent) =

Answer 14

m(solvent)/V(of solution)

Question 15

density (of solution) =

Answer 15

mass (of solution)/V (of solution) [g/cm^3]

Question 16

stoichiometry

Answer 16

mass relationships between substances in a chem reaction (based on mole ratio - coefficients in a balanced chem equation)

Question 17

pV=

Answer 17

nRT [Pam^3=molJ/Kmol*K]

Question 18

R=

Answer 18

8.314 J/Kmol

Question 19

standard condition formula for n:

Answer 19

n= V^0/V^0ˇm (V is the volume of the gas, Vˇm is the standard molar volume (22.7 dm^3/mol)

Question 20

1 mol of gas at STP is…

Answer 20

…22.7 L. - Tˇ0=0°C or 25°C, Pˇ0=1 atm (101.3 Pa)