Exam #3 first class

can go from mass of reactants to mass of reactants. true or false

TRUE

can go from product to product, true or false

TRUE

We "count" out the right number of molecules by weighing them because (for example in c3h8 + 5o2 → 3co2 + 4h2o)

a molecule of propane does not weigh the same as a molecule of o2 or co2 or h2o

1 mole of propane reacts with 5 moles of o2 to make 3 moles of carbon dioxide and four moles of water and 6.022 × 10 ^23 molecules of c3h8 3.01 x 10^24 molecules of o2 1.8 x 10^24 molecules of co2 2.4 x 10 ^24 molecules of h2o

are equivalent ways of saying the equation c3h8 + 5o2 → 3co2 + 4h2o

To interpret the molecules in a chemical equation, we use

avagadaro's number 6.022 × 10 ^23

May need unit conversions in math stoichiometry problem at

beginning (before step 1) or end (after step 3)

Balance c3h8 + o2 → co2 + h2o

c3h8 + 5o2 → 3co2 + 4h2o

Write propane reacts with oxygen to make carbon dioxide and water vapor symbolically

c3h8 + o2 → co2 + h2o

can multiply through the _____________________ in chemical equations as long as _______________________

coefficients; pertains to every molecule/element

in our lab, there is sut on aluminum can because

combustion reaction doesn't have enough oxygen to go all the way to carbon dioxide

can think of molecular weights as

conversion factors

carbon monoxide is dangerous to humans, and can form from the reaction of c3h8 + 5o2 → 3co2 + 4h2o if...

don't have adequate number of moles of o2 in reactant, so cannot make enough oxygen in co to be co2

writing 1 mol c3h8/3 mol co2 doesn't mean ________________ but rather means_________________ in the equation of c3h8 + 5o2 → 3co2 + 4h2o

equivalent in mass but rather equivalent in this particular equation

in order to use the values we get for mass from periodic table, all math of products/reactants must be in

grams not lbs or kg

All numbers on periodic table of elements in terms of mass are in

grams per mole

example of going from mass of reactants to mass of reactants c3h8 + 5o2 → 3co2 + 4h2o

have to have 5x the number of moles of propane for oxygen in order to make that amount of co2

example of going from mass of reactants to mass of reactants important because c3h8 + 5o2 → 3co2 + 4h2o

have to have 5x the number of moles of propane for oxygen in order to make that amount of co2 if not, will make carbon monoxide

thermodynamics with stoichiometry can calculate

how much heat is released using heat as reactants or products in same way we are using molecular weights and masses

Define law of conservation of mass

if we have the same number of atoms on both sides, then the total mass of the reactants has to equal the total mass of the products

the balanced equation can give you a lot of

information and conversion factors

Why do we interpret mass in a chemical equation

mass is what we can measure, we can't count out molecules or atoms -can weigh them via molecular weight

can go from mass of reactants to mass of products AND

mass of products to mass of reactants

in math stoichiometry problems, cannot go directly from

mass of the reactant to mass of the product

basic summary of stoichiometry

mass to moles then moles to mass

reactant to reactant reactant to product product to reactant product to product all have the same way of

math

The chemical reaction/equation is talking about the

mole ratio of our reactants and products

balanced equations are simply showing the

mole ratios of the species involved

How to find the number of molecules in a chemical equation

multiply the number of moles (coefficient) by avagadaro's number

gas grills and furnaces can malfunction and produce carbon monoxide because

not getting enough oxygen during the combustion (toxic)

"BBQ in Chemistry" propane reacts with _______________ to make _______________ & _________________

oxygen to make carbon dioxide & water vapor

Example of least common multiple to get oxygen atoms the same on both sides fe + o2 → fe2o3

put 6 oxygen atoms on both sides 3o2 → 2fe2o3

most of the time in lab, we are given the mass of the _________________ to find the mass of the ________________

reactant to find the mass of the product

4 ways all reactions can occur

reactant to reactant reactant to product product to reactant product to product

even if you don't have enough moles of a certain molecule or element, then the reaction will

still occur

Practical application- we can determine how much carbon dioxide we put in to the air via

stoichiometry

if don't have enough moles of o2 in c3h8 + 5o2 → 3co2 + 4h2o even less than that would make carbon monoxide, you will make ______ because...

sut (just carbon) bc starved the reaction for oxygen sut clogs furnace

Use the molecular weight to connect

the balanced chemical equations with the masses that we can measure in the labratory

writing 1 mol c3h8/3 mol does not mean

the masses are the same

The law of conservation of mass still applies in chemical equations, however

the masses of the different groupings of molecules/atoms do not weigh the same thing

if we have the same number of atoms on both sides, then

the total mass of the reactants has to equal the total mass of the products (Law of conservation of mass)

molecular weights can be conversion factors because

they are what allow us to convert between mass and moles

stoichiometry is useful in carbon footprint

to calculate co2 annual emission we can determine how much carbon dioxide we put in to the air from coal, petroleum, and natural gas we are combusting

One of the applications of the Law of conservation of is

to chemical equations

We rarely have the exact masses, thus we

use mole ratio (balanced eq.) and molecular weight (PT) to determine mass equivalencies

Why do we do stoichiometry problems

use the mole ratios (from the balanced equations) and the molecular weights (from the periodic table) to determine mass equivalencies

prof. k used stoichiometry in which experiment and why?

washers lab, to make sure we had way more moles of HCl to dissolve zinc than needed

sometimes in lab, we need to find the mass of the reactants because

we need a specific mass for the product

connect what's going on molecularly in the reaction and what we can physically do in the lab by

"count" out the right number of molecules by weighing them

Find the molecular weight of propane (c3h8)

(36 + 8) 44 g c3h8/1 mol

Steps to systematically writing balanced equations: two parts to Step 2

-Leave the elements for last (unless more elements than anything else) -If you put coefficients in front of the elements, it doesn't change any other type of atom

Step 2 in math stoichiometry problem

-convert that ^ to moles of that reactant (mol) (mole ratio from balanced equation) -moles of a product (mol)

Another way to write 4fe + 3o2 → 2fe2o3 using fractional coefficients

2Fe + 3/2 o2 → Fe2o3

In one mole of propane (c3h8) there are how many moles of carbon atoms

3

find molecular weight of o2

32 g/mol o2

How many grams of Carbon in 1 mole of propane (c3h8)

36gC/1 mole c3h8

write out and interpret molecular weights for the following equation c3h8 + 5o2 → 3co2 + 4h2o

44g of c3h8 reacts with 160g of o2 react together to make 132g of co2 and 72g h2o

because the LCM of oxygen changes the chemical equation to fe + 3o2 → 2fe2o3, must now balance the fe by

4fe + 3o2 → 2fe2o3

doesn't have to just be 1 mol c3h8/3 mol co2 also could apply to: in the reaction of c3h8 + 5o2 → 3co2 + 4h2o

5 mol o2/1 mol c3h8 (reactant to reactant)

Practice problem: Burn 50 grams of propane in the air (so plenty of oxygen) How much water vapor/what mass of water (h2o) vapor do we make if we burn 50g of propane (c3h8)

50x4x18 divided by 44 = 81.81 g h2o

Interpret c3h8 + 5o2 → 3co2 + 4h2o in terms of molecuels

6.022 × 10 ^23 molecules of c3h8 react with 3.01 x 10^24 molecules of o2 those two quantities of things react to make 1.8 x 10^24 molecules of co2 and 2.4 x 10 ^24 molecules of h2o

How many molecules in each? c3h8 + 5o2 → 3co2 + 4h2o

6.022 × 10 ^23 molecules of c3h8 3.01 x 10^24 molecules of o2 1.8 x 10^24 molecules of co2 2.4 x 10 ^24 molecules of h2o

Balance photosynthesis co2 + h2o → c6h12o6 + o2

6co2 + 6h2o → c6h12o6 + 6o2

How many grams of Hydrogen in 1 mole of propane (c3h8)

8gH/1 mol c3h8

NO chemical reaction/equation says how

ATOMS go together or react with molecules

cannot go from mass of the reactant to mass of the product in stoichiometry because

-mole ratio is not necessarily one -molecular weights aren't necessarily the same

Step 3 in math stoichiometry problem

-moles of a product (mol) (molecular weight from periodic table) -mass of a product

Steps to systematically writing balanced equations: three parts to Step 1

-start out with most complicated formula -one atom at a time, don't freak out -smallest coefficients

Step 1 in math stoichiometry problem

-start with mass of a reactant (g) (molecular weights from pt) -convert that ^ to moles of that reactant (mol)

It is acceptable to have (example oxygen)

1 & 1/2 moles of oxygen atoms

the balanced equation can give you conversion factors because example in the reaction of c3h8 + 5o2 → 3co2 + 4h2o

1 mol c3h8 (is equivalent to) 3 mol co2 also written as 1 mol c3h8/3 mol co2 not equivalent in mass, but equivalent in this particular equation

1 mol c3h8/3 mol co2 means

1 mol of propane is going to make one mole of co2 if i make a certain number of moles of co2, then i can calculate how many moles of propane must have burned in order for that to be the same

Interpret c3h8 + 5o2 → 3co2 + 4h2o in terms of moles

1 mole of propane reacts with 5 moles of o2 to make 3 moles of carbon dioxide and four moles of water

We use mole concept instead of molecule concept when writing chemical equations because for example c3h8 + 5o2 → 3co2 + 4h2o

1 mole of propane reacts with 5 moles of o2 to make 3 moles of carbon dioxide and four moles of water is easier to interpret than 6.022 × 10 ^23 molecules of c3h8 3.01 x 10^24 molecules of o2 1.8 x 10^24 molecules of co2 2.4 x 10 ^24 molecules of h2o

In order to do stoichiometry problems, what two things do you need

1. balanced equation 2. molecular weights of all the "stuff" in the balanced equation

We interpret chemical equations in what 3 ways

1. moles 2. molecules 3. mass

Why is it not atoms going together in a chemical equation? example 2Fe + 3/2 o2 →Fe2o3

Fe and Fe2o3 is iron solid and 1 atom of iron is not solid iron 1 atom of iron is just by itself in the gas phase