reactivity 2.1

Question 1

in combustion reactions of organic compounds, in which order do you balance H, C and O?

Answer 1

C, H, O

Question 2

what are the masses of reactants useful for determining?

Answer 2

how much of the reactants exactly react with each other to prevent waste

Question 3

define the stoichiometry of the reaction

Answer 3

the ratio of moles of all the reactants and products

Question 4

things needed to find the mass of products formed in a reaction x3

Answer 4

mass of reactants, molar mass of reactants AND the balanced equation

Question 5

at STP one mole of any gas has what volume? (molar gas volume)

Answer 5

22.7 dm³ mol⁻¹

Question 6

how to determine which gas is the limiting reactant in an equation?

Answer 6

divide the volumes of the gases by the coefficients and whichever gives the lowest number is the limiting reactant

Question 7

how to find the volume of a given number of moles of gas

Answer 7

volume of gas (dm³) = amount of gas (mol) x 22.7 dm³ mol⁻¹

Question 8

how to find the number of moles of a given volume of gas

Answer 8

amount of gas (mol) = volume of gas (dm³) / 22.7 dm³ mol⁻¹

Question 9

define volumetric analysis

Answer 9

a process that uses the volume and concentration of one chemical reactant (a standard solution) to determine the concentration of another unknown solution

Question 10

four steps in calculating concentration

Answer 10

1. write balanced equation
2. determine known values of substances
3. deduce mole ratios
4. calculate unknown values of substances

Question 11

equation to determine moles from volume and concentration

Answer 11

moles = volume (dm⁻³) x concentration

Question 12

purpose of a back titration

Answer 12

to find the concentration/amount of an unknown substance by using an excess of a further reactant (i.e. an acid/alkali)

Question 13

3 steps to determine which reactant is limiting

Answer 13

1. calculate number of moles of the reactants (n=m/MM)
2. write balanced equation
3. divide moles by coefficient to determine the limiting reagent (lowest # is limiting)

Question 14

3 reasons that not all reactants react to form products during a reaction

Answer 14

other reactions may take place simultaneously, reaction does not go to completion OR products are lost during separation & purification

Question 15

what does the percentage yield show?

Answer 15

how much of a particular product you get from the reactants compared to the maximum theoretical amount that you can get

Question 16

how to calculate percentage yield

Answer 16

% yield = (actual yield / theoretical yield) x 100

Question 17

define actual yield

Answer 17

the number of moles or mass of product obtained experimentally

Question 18

define theoretical yield

Answer 18

the number of moles or mass obtained by a reacting mass calculation

Question 19

define atom economy (of a reaction)

Answer 19

how many of the atoms used in the reaction become the desired product (the rest of the atoms/mass is wasted)

Question 20

how to find atom economy from a balanced equation? what is the equation?

Answer 20

by calculating Mᵣ (relative formula mass) of the desired product
atom economy = (molecular mass of desired product / sum of molecular masses of all reactants) x100

Question 21

in what type of reaction will the atom economy always be 100%? why?

Answer 21

in addition reactions because all of the atoms are used to make the desired product (whenever there is only one product, atom economy = 100%)

Question 22

how to calculate atom economy using mass?

Answer 22

atom economy = (mass of the desired product formed / total mass of all reactants) x 100

Question 23

efficient processes have ___ atom economy. why x2?

Answer 23

high, they use fewer resources AND create less waste

Question 24

aside from atom economy and % yield, what other factors can be used to measure efficiency of a chemical process? x4

Answer 24

rate, quantities of reagents, energy uses AND economic efficiency