Stoichiometry (5b), Study notes of Stoichiometry

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Stoichiometry (5b)

Mole Ratios Pogil Per 7

March 3rd, 2020

Agenda 3/3/2020 Period 7

● Weighing out a mole of water (hands on

activity)

○ How many now? (thinking with looking)

● Mole Ratios Pogil

○ Correct 1-

● Quick check and turn in Mole Ratios Pogil

However, in real life the reaction represented by an

equation occurs an unimaginable number of times.

Short of writing very large numbers (

or larger) in

front of each chemical equation, how can we

interpret chemical equations so that they more

realistically represent what is happening in real life?

In this activity you will explore the different ways a

chemical reaction can be interpreted.

Model 1. A Chemical Reaction N

(g) + 3 H

(g) → 2 NH

(g)

1. a) Coefficients for N

H

NH

2. a) Calculate the amount of reactants consumed

and products made.

N 2 consumed

H 2 consumed

NH 3 produced Ratio N 2 :H 2 : NH (^3)

For a single reaction, how many molecules of each substance would be consumed or produced?

molecule

molecule s

molecules

If the reaction occurred one hundred times, how many molecules would be consumed or produced?

molecule s

molecule s

molecules

If the reaction occurred 538 times, how many molecules would be consumed or produced?

molecule s

molecule s

molecules

3. a) How do the reduced ratios in the last column

compare to the coefficients in the reaction shown in

Model 1?

The reduced ratio is always the same as

the coefficients in the balanced equation

for the reaction.

4. Even 538 is a small number of molecules to use in

a reaction. Typically chemists us much larger

numbers of molecules. Recall that one mole is equal

to 6.02 x 10

particles.

4. a) Calculate the amount of reactants consumed

and products made.

N 2 consumed

H 2 consumed

NH 3 produced Ratio N 2 :H 2 : NH (^3)

If the reaction occurred 6.02 x 10 23 times, how many molecules would be consumed or produced?

6.02 x 10 23 mole cules

1.86 x 10 24 molecule s

1.204 x 10 24 molecules

How many moles of each substance would be consumed or produced in the previous situation?

1 mole 3 moles 2 moles 1:3:

5. b) Use mathematical concepts to explain how your

answer in part a) is possible.

Each part of the ratio of coefficients for

the chemical reaction was multiplied by

the same number, so the reduced ratio

stays the same.

6. The ratio obtained from the coefficients in a

balanced chemical equation is called the mole ratio.

a) Mole Ratio is 1 N 2

: 3 H 2

: 2 NH 3

b) Explain why this ratio is called a mole

ratio.The ratio is the number of moles

of reactants and products you would

need or make if the reaction occurred

6.02 x 10

23 times.

7. Setting up proportions to solve chemical problems

b) How many moles of NH 3

could be

made by completely reacting 9.00 moles

of H 2

?

x moles NH 3

= 2 moles NH 3

9.00moles H 2

3 moles H 2

So x = 6 moles NH

7. Setting up proportions to solve chemical problems

c) How many moles of H 2

would be

needed to react completely with 7.

moles of N 2

?

x moles H 2

= 2 moles H 2

7.41moles N 2

1 mole N 2

So x = 22.2 moles H

9. a) Can the mole ratio from a balanced chemical

equation be interpreted as a ratio of masses?

No, the mass ratio does not match the

coefficients from the balanced chemical

equation.

9. a) Can the mole ratio from a balanced chemical

equation be interpreted as a ratio of masses?

b) Since each substance in the reaction has a

different molar mass, the original ratio from the

coefficients is multiplied by three different

numbers to find the number of grams consumed

or produced. Therefore, the mass ratio is no

longer the same as the ratio of coefficients.