stoich s2015

Nickel III dichromate reacts with calcium

Write and balance

When you are done: Read IN YOUR LIFE on Pg 279 then see #1

Stoichiometery

Unit 6 Ch 9

Read 278-316Mole-mole Mole-gram Gram-gram gram –Liters of gas @STP

% yield limiters Heat

Day 1

What is stoichiometry?• This is the process of using balanced

equations to calculate the mole ratios and calculating the amounts used, created, or left over, in a chemical experiment.

• If we are given a reaction and one piece of information, we can find out ALL the rest!

What is stoichiometry?• We use the balanced equation to do a mole-

mole conversion. This way we can predict what quantities we can get when working in the lab. We call this the theoretical yield.

12.1

Mass Conservation in Chemical Reactions

– Mass and atoms are conserved in every chemical reaction.

– Moles don’t have to be conserved, but MASS does! (see next slide)

Relationships given from a rxn.

• 6HCl (aq) + 2Al (S) 3H2 (g) + 2AlCl3 (Aq)

6 molecules HCl + 2 Al atoms 3 molecules H2 + 2 Form. Units of AlCl3

6 Moles HCl + 2 moles Al 3 moles H2 + 2 mole of AlCl3

218.76 g HCl + 53.96 g Al 6.06 g H2 + 266.66 g of AlCl3

In the reaction

• 2H202 2H20 + 1O2

• We can write several mole relationship that can be used as conversion facts.

For example in this equation,

• 2H20 + 2Na 2NaOH + H2 (g)

• Can you describe this reaction to your partner?

• 2 moles of water will combine with 2 moles of sodium to make 2 moles of sodium hydroxide and 1 mole of hydrogen gas.

Sample class problems(see pg 2 of packet)

2Li + FeS Li2S + Fe

•Write relationships

Sample class problems

2Li + FeS Li2S + Fe

•If you have 4.5 moles of Li, how many moles of Lithium sulfide can be produced?


2Li + FeS Li2S + Fe

•If you have 4.5 moles of Li, how many moles of Iron can also be produced?


2Li + FeS Li2S + Fe

If you used 35.5 grams of Lithium how many moles of FeS would be required to make it all react perfectly?

Another example: calculate


• If you had 0.450 moles of Al, how many moles of HCl would you need to completely react with it?

0.450 mol? mol

Another example: calculate


• If you had 0.450 moles of Al, how many moles of each product would you produce.

0.450 mol ? mol ? mol

TERMS (fill in your vocab)

• Mole ratio (we just did some)

Mole Ratio

• The ratio of moles of one substance to another from a balanced equation (coefficients)

Limiting reagent

• Any reactant that is used up first in a chemical reaction; it determines the amount of product that can be formed in the reaction.

Theoretical yield

• The amount of product that could form during a reaction calculated from a balanced chemical equation; it represents the maximum amount of product that could be formed from a given amount of reactant

Actual yield

• The amount of product that forms when a reaction is carried out in the laboratory

Percent yield

• The ratio of actual yield to the theoretical yield for a chemical reaction expressed as a percentage; a measure of the efficiency of a reaction

Excess reagent• A reagent present in a quantity that is

more than sufficient to react with the limiting reagent; any reactant that remains after the limiting reagent is used up in a chemical reaction

Calorimeter

• an apparatus for measuring the amount of heat involved in a chemical reaction

Sample problems mole to mole

• I react 0.1 mol of KI with excess Pb(NO3)2, how many moles of each product will I get?

• COPY DOWN MY “ROAD MAP”

Roadmap

We might be given moles, mass, volume or # of particles.

Use mole ratio from the balanced equation.

Roadmap cont.

These values are found from the periodic table. Be sure to put correct labels on everything. Your teacher is very picky about this.

BACK TO THE PROBLEM


• WRITE THE EQUATION & BALANCE IT.

Here is the equation


• Pb(NO3)2 + KI PbI2 + KNO3

Now it is balanced


• Pb(NO3)2 + 2KI PbI2 + 2KNO3

Put in the given information



0.1 molexcess ? mol ? mol

Write what you are given and want to find

above the reaction.

Solve it using dim. AnalysisSHOW ALL WORK & LABELS


0.1 molexcess ? mol ? mol

0.1 mole KI 1 mol PbI2 =

2 mole KI

0.1 mole KI 2 mol KNO3 =

2 mole KI

Sample problem gram to gram

• I react 1.2 grams of zinc with excess HCl, How many moles of each product will I get?

• Let’s do this on the board

In class practice• Spring 2015 packet page 3 (get on

it in class) (adjusted to did # 4 in class, do 1-3 & 2nd part of #4)

• Then read pgs 279- 287 do pg 287 #1,2,4,5

Limiting Reagents

• In a chemical reaction, an insufficient quantity of any of the reactants will limit the amount of product that forms. – The limiting reagent is the reagent that

determines the amount of product that can be formed by a reaction.

Limiting Reactant

• You will be given various amounts and you need to see which one is in excess. Then use the limiting reagent to answer the questions.

• To start with, I suggest picking one reactant and going to the other one.

Day 2

Sample limiting


25 g35.00 g ? grams

35.00 g Pb(NO3)2 1 mol Pb(NO3)2 2 mol KI 166g KI = g KI

331.22 g Pb(NO3)2 1 mol Pb(NO3)2 1 mol KI

Our answer would be the required amount of KI needed. Do we have enough?

Solve the problem using the “limiter”


25 g35.00 g ? grams

25 g KI 1 mol KI 1 mol PbI2 461 g PbI2 = g PbI2

166g KI 2 mol KI 1 mol PbI2

Limiter Trick

Go back to this


25 g35.00 g ? grams

Read pg 296-304

• Let’s look at this example.

Sample

Worksheet Limiters (answers available)

•#56 pg 315

•WS

Limiter WS Solutions

Lim ans

Percent Yield

• The theoretical yield is the maximum amount of product that could be formed from given amounts of reactants.

• In contrast, the amount of product that actually forms when the reaction is carried out in the laboratory is called the actual yield.

Day 2 or 3

The percent yield is the ratio of the actual yield to the theoretical yield expressed as a percent.

You try

Try percent problems in packe

• # 4 is more challenging.

Quiz

• Complete the rest of the limiter worksheet

• Mini-quiz

Stoich of Heat

• Sec 10.3 SEE PG 334 EX 10.5

• 29-31 pg 354

• Heat content or enthalpy is denoted by ∆H. The ∆H associated with an equation tells you the amount of heat either absorbed or released when a chemical reaction occurs.

• ∆H can either be negative or positive. The sign on ∆H lets you know if the reaction is endothermic or exothermic in nature. Recall that endothermic reactions are those that absorb energy from the surroundings. Exothermic reactions are those that give off energy in the form of heat.

• Exothermic Reaction:2 B (s) + 3 H2 (g) + 3 H2O (g) -->

B2H6 (g) + 3 H2O (l) ∆H = -96 kJ• When the equation is written this way, it shows that the

reaction is exothermic as the sign on ∆H is negative.

• Alternatively, you may see the equation written in this manner:

2 B (s) + 3 H2 (g) + 3 H2O (g) -->

B2H6 (g) + 3 H2O (l) + 96 kJ

• Endothermic Reaction:4 NO2 (g) + 6 H2O (l)

4 NH3 (g) + 7 O2 (g) ∆H = 1396 kJ

• Since the sign on ∆H is positive, we can tell we're looking at a reaction which is endothermic. (we need to ADD this amount of heat to make it go)

• Another way this can be represented is:

• 1396 kJ + 4 NO2 (g) + 6 H2O (l) 4 NH3 (g) + 7 O2 (g)

• In this case, the amount of energy is embedded in the equation as a reactant, indicating that energy must be absorbed or taken in so that the reaction can occur.

2 B (s) + 3 H2 (g) + 3 H2O (g) B2H6 (g) + 3 H2O (l) ∆H = -96 kJ

• Ex: How much energy is released when 73.2 g of B react as illustrated above?

Let’s try a couple

• How much heat is given off when 450.0 grams of Propane are burned completely as shown in this reaction?

• C3H8 + O2 CO2 + H2O ΔH = -2,220.1 kJ/mol

• TRY THESE ON THE WORKSHEET (Answers provided)

• THEN # 29-31 pg 354

Try the Stoich WS

• 3 problems in class.

• THEN worksheet Some like it hot (homework) 1-3.

• Review for a stoich test.

Challenge

• Heat of dissolving NaOH calculate the final temperature that can be reached.

Stoich of Heat

Stoich of Heat

• Cheeto Lab– Heat lost= heat gained.

– Calories are a unit of heat– 1000 calories = 1 Kilocalorie (Calories)

– Calculate Calories

Be able to

• Convert to and from

• Mole ratio: mole-mole

• Mass: g-g

• Volume gas @stp

• Heat kJ

• % yield and limiters

• Test has 5 questions.

stoich s2015

Education

moles al

moles of al

moles hcl

moles of hcl

moles of fes

ratio of moles

moles h2

moles of iron