Ch Stoichiometry Mole to Mole Conversions

Interpreting Chemical Equations

Balanced Equations Why do we need balanced equations? To observe the law of conservation of matter Because: -what goes in must come out -nothing can be created or destroyed

Ways to Interpret a Chemical Equation There are three ways to interpret a chemical equation: 1. By particle 2. By mole 3. By mass

Balanced Equation- By Particle We can read a chemical equation using particles. Look at this equation: Na 2 O + H 2 O → 2NaOH We would read this as: one formula unit of sodium oxide plus one molecule of water produces two formula units of sodium hydroxide. Remember coefficients tell you how many particles there are of each element or compound.

Balanced Equation- By Mole We can also read a chemical equation using moles in place of particles. In this case we are simply multiplying the entire equation by 6.02x10 23 Look at the following equation: Na 2 O + H 2 O → 2NaOH We could read this equation as: one mole of sodium oxide plus one mole of water produces two moles of sodium hydroxide. In this case, coefficients would tell you how many MOLES of a particular element or compound were present.

Balanced Equations-By Mass Lastly, we can read an equation by mass using the molar mass of each substance present rather than number of particles or moles. Aside from maintaining the same number of each element (shown by balancing an equation), we can prove that matter (or mass) has not been created or destroyed. Look at this equation: Na 2 O + H 2 O → 2NaOH

Na 2 O + H 2 O  2NaOH To show that mass is conserved, we could list the molar masses of each substance 62.0 g Na 2 O g H 2 O  2(40.0 g NaOH) 80.0 g reactants  80.0 g products Is mass conserved?

Stoichiometry

What is it? The study of the quantitative, or measurable, relationships, that exist in chemical formulas and reactions.

Stoichiometry Used to predict how much product will be produced Used to tell how much reactant will be needed

Why do we need Stoichiometry? To Convert moles of one compound to moles of another compound The mole is the only thing that all substances have in common Therefore…. Mole is the only unit that can get you from one compound to another Mole ratio

Balanced Equations Balancing equations is VERY necessary in order to maintain the law of conservation of mass! What do the coefficients mean? How many of each of the reactants and products we have (can be either particles or moles) Coefficients in a BALANCED EQUATION set up the mole ratio 2H 2 + O 2  2H 2 O

Balanced Equations Here is a reaction for rocket fuel N 2 H 4 + 2H 2 O 2 → N 2 + 4H 2 O In terms of moles: 1 mole N 2 H moles H 2 O 2  1 mole N moles H 2 O Looking at the balanced equation the coefficients are 1:2:1:4

We need these MOLE RATIOS! If you know the actual number of moles of one of the substances in the balanced equation, you can determine the number of moles of the others substances too…using the MOLE RATIO.

Mole Ratios You can set up the mole ratios as conversion factors between each reactant/product in the reaction. N 2 H 4 + 2H 2 O 2 → N 2 + 4H 2 O

Stoichiometry Steps Step 1: Balance the equation Step 2: Write down what the question gives you Step 3: Determine the conversion factor needed Step 4: Solve (multiply across the top, divide by the bottom)

Let’s say we want to know how many moles of water can be produced if we have 6.0 moles of oxygen gas, O 2. Step 1: Balance Equation 2H 2 + O 2  2H 2 O Step 2: We know we have 6.0 moles O 2 Step 3: What is the ratio between O 2 and H 2 O? 1 mole O 2 will produce 2 moles of H 2 O 1 mole O 2 2 moles H 2 O OR 1 mole O 2 2 moles H 2 O

Step 4: Solve. Use dimensional analysis just like before: 6.0 mol O 2 x 2 mol H 2 O 1 mol O 2 =12 moles H 2 O Yes, you still have to set it up using dimensional analysis!!!!!

Practice Problem #1: NH 4 NO 3  N 2 O + 2H 2 O a) You have 4.2 moles of NH 4 NO 3 reacting, how many moles of H 2 O are produced? 1. Balance equation 2. Write what you have 3. Determine conversions 4. Solve 4.2 mol NH 4 NO 3 x ___________ = 2 moles H 2 O 1 mole NH 4 NO moles H 2 O

NH 4 NO 3  N 2 O + 2H 2 O b) How many moles of N 2 O are produced? 4.2 moles NH 4 NO 3 x ___________ = 1 mole N 2 O 1 mole NH 4 NO moles N 2 O

Practice Problem #2: __HCl + __Zn  __ZnCl 2 + __H 2 How many moles of HCl are needed to react with 2.3 moles of Zn? 2.3 mol Zn x ___________ = 1 mole Zn 2 moles HCl 4.6 moles HCl

Practice Problem #3: How many moles of Al(NO 3 ) 3 will be produced when 0.75 mol AgNO 3 react according to the following equation: __AgNO 3 +__Al →__Al(NO 3 ) 3 +__Ag Follow the steps to set it up