# Mole relationships in chemical equations

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Mole relationships in chemical equations

DO-NOW – Silent and Independent!
Remember: (g) = gas (l) = liquid (s) = solid (aq) = aqueous Must use rules for naming/writing formulas Ionic compounds – balance charges, NO prefixes Covalent compounds – use prefixes

Information from Chemical Equations
To produce fertilizers, Nitrogen gas is combined with Hydrogen gas to produce Nitrogen trihydride (ammonia). N2(g) + H2(g)  NH3(g)

Information from Chemical Equations
Making fertilizer uses a lot of energy and a lot of raw materials Efficiency is key!! How can knowledge about chemical reactions make This process as efficient as possible?

The Law of Conservation of Mass
In a chemical reaction, matter is never created or destroyed. The number of atoms and the mass of the reactants must be equal to the number of atoms and the mass of the products.

Mini-Lab! NaHCO3(s) + CH3COOH(aq)  CO2(g) + H2O(l) + NaCO3(aq)
Baking soda reacts with acetic acid (vinegar) to produce… Carbon dioxide gas, liquid water, and sodium carbonate solution Initial mass: Final mass:

Mini - Lab Find the mass of both reagents IN THEIR CONTAINERS.
Record this mass as your initial mass Remove materials from balance Carefully pour the acetic acid into the baking soda. Agitate until bubbling stops Find the mass of both reagents IN THEIR CONTAINERS again. Record this mass as your final mass

What were your results? Thoughts? Why doesn’t this reaction seem to obey the law of conservation of mass? What could we do to confirm that it satisfies the law of conservation of mass?

More examples: Law of Conservation of Mass
CS2(l) + O2(g)  CO2(g) + SO2(g) If I reacted 5 grams of CS2 with 5 grams of O2, and the reaction produced 2 grams of CO2, how many grams of SO2 must have been produced? If my products had a total mass of 20 grams, how many grams of reactants must I have started with? If I reacted 3 grams of CS2 with an unknown number of grams of O2 and produced a total of 4 grams of products, what was the mass of the O2?

Balancing Chemical Equations
How do we show, in a chemical equation, that the law of conservation of mass is being obeyed? The law of conservation of mass must be satisfied by equalizing the number of atoms on the reactant and the product sides. Use coefficients to show how many molecules of each compound.

H2(g) F2(g)  HF(g) H2(g) F2(g)  HF(g) 2

Rules for balancing an equation
1. Only change the coefficients that appear in front of an element or compound 2. Never change any subscripts in a formula 3. Coefficients should be written as the lowest possible ratios 4. Begin by balancing elements that appear ONLY once on each side of the equation

H2O(l)  H2(g) O2(g) H2O(l)  H2(g) O2(g) 2 2

Balancing Chemical Equations
Ca(s) S8(s)  CaS(s) 8 Ca(s) S8(s)  CaS(s) 8

2 Zn(s) + HCl(aq)  ZnCl2(aq) + H2(g)

Na2O H2O  NaOH O2

2Na2O H2O  NaOH O2

CaCl2 + Fe2(SO4)3  CaSO4 + FeCl3

3CaCl2 + Fe2(SO4)3  3CaSO4 + 2FeCl3

Liquid silicon tetrachloride reacts with liquid water to produce solid silicon dioxide and a solution of hydrochloric acid (HCl). Write the chemical equation for this word equation Balance it

SiCl4(l) + 2H2O(l)  SiO2(s) + 4HCl(aq)

Mole Ratios in Chemical Equations

Building a Tricycle To build a tricycle, you need a frame, a seat, 3 wheels, a set of handlebars and 2 pedals If I wanted to build 2 tricycles, How many seats would I need? How many wheels? What if I wanted 346 tricycles?

Balanced Chemical Equations
Chemical equations are our recipes for chemical reactions! Balanced chemical equations can be used to calculate how much reactant we will use or how much product is formed from a chemical reaction

Coefficients indicate relative numbers of moles or molecules of reactants and products.
H2(g) + Cl2(g)  2HCl(g) One mole of hydrogen reacts with one mole of chlorine gas to yield two moles of hydrogen chloride gas. OR: One molecule of hydrogen gas reacts with one molecule of chlorine gas to yield two molecules of hydrogen chloride gas.

N2(g) +3H2(g)  2NH3(g) Number of Molecules – look at coefficients:
1 molecule of N2 3 molecules of H2 2 molecules of NH3 Just like with atoms, it makes more practical sense to use Avogadro's number (1 mole) of molecules rather than individual molecules

N2(g) +3H2(g)  2NH3(g) Number of Moles – look at coefficients:
1 mole of N2 3 moles of H2 2 moles of NH3 Note that the number of moles (like the number of molecules) is not the same on both sides!

Na2O(s) + 2CO2(g) + H2O(g)  2NaHCO3(s)
How many moles of sodium oxide? How many moles of carbon dioxide? How many moles of water vapor? How many moles of sodium hydrogen carbonate?

Mole Ratios What is the RATIO between tricycle seats and tricycle wheels? 1 seat : 3 wheels 1 seat 3 wheels Using the fractional form of the ratio is going to make a lot more sense in chemistry

Mole Ratios N2(g) +3H2(g)  2NH3(g) What are the mole ratios between:
moles of N2 and moles of H2? moles of NH3 and moles of N2? moles of H2 and moles of NH3? 1mol N mol NH mol H2 3mol H mol N mol NH3

2H2O(l)  2H2(g) + O2(g) How many moles of water?
How many moles of oxygen gas? How many moles of hydrogen gas? Mole ratio of water to hydrogen gas. Mole ratio of oxygen gas to hydrogen gas.

CS2(l) + 3O2(g)  CO2(g) + 2SO2(g)
How many moles of oxygen gas? How many moles of carbon dioxide gas? Mole ratio of oxygen to carbon dioxide. Mole ratio of carbon disulfide to oxygen. Mole ratio of carbon dioxide to sulfur dioxide.

4Fe(s) + 3O2(g)  2Fe2O3(s) Mole ratio of iron to oxygen gas.
Mole ratio of oxygen gas to iron (III) oxide. Mole ratio of iron (III) oxide to iron.

N2(g) +3H2(g)  2NH3(g) How many moles of ammonia will I get by reacting 2 moles of nitrogen gas? 2mol N2 x 2 mol NH3 = 4 mol NH3 mol N2 The ONLY way to relate amounts of two different substances is to use the MOLE RATIO!! GIVEN MOLE RATIO

MOLE  MOLE conversions
To get from moles of substance A to moles of substance B, always use the mole ratio! STEP 1: Write the given value (with a unit) over 1 STEP 2: Write a blank conversion factor STEP 3: Fill in the units to cancel your given unit STEP 4: Complete the mole ratio STEP 5: Multiply/Divide to get final answer

How many moles of nitrogen gas react with 12 moles of hydrogen gas?
N2(g) +3H2(g)  2NH3(g) How many moles of nitrogen gas react with 12 moles of hydrogen gas? 12 mol H2 x 1 mol N2 = 4 mol N2 mol H2 The ONLY way to relate amounts of two different substances is to use the MOLE RATIO!! GIVEN MOLE RATIO

4Fe(s) + 3O2(g)  2Fe2O3(s) How many moles of oxygen gas react with 4 moles of solid iron? How many moles of iron (III) oxide are produced by the reaction of 3 moles of oxygen gas? How many moles of solid iron are required to react with 3 moles of oxygen gas? How many molecules of iron (III) oxide are produced by the reaction of 4 molecules of solid iron?

CS2(l) + 3O2(g)  CO2(g) + 2SO2(g)
How many molecules of CS2 react with 9 molecules of O2? How many molecules of O2 react with 2 molecules of CS2? How many moles of CO2 are produced by the reaction of 3 moles of CS2? How many moles of SO2 are produced by the reaction of 12 moles of O2?