Practice Excess Reactant in Chemistry

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

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Quick Recap

The reactant that remains after a reaction stops because the limiting reactant has been used up.

If one ingredient runs out first, the other one is left over.

Showing a random 20 of 50 problems.

Example 1

medium

2H_2 + O_2 \rightarrow 2H_2O

10\text{ mol}

H_2

and

4\text{ mol}

O_2

react. How many moles of

H_2

remain at completion?

Example 2

easy

A + B \rightarrow C

(1:1),

3\text{ mol}

A

and

7\text{ mol}

B

react. Which is the excess reactant?

Example 3

challenge

A + 3B \rightarrow 2C

, mixing

x

mol

A

with

7\text{ mol}

B

leaves

1\text{ mol}

B

in excess. Find

x

(assume

A

is limiting).

Example 4

challenge

A mixture of

0.3\text{ mol}

H_2

and

0.3\text{ mol}

O_2

is sparked. Reaction:

2H_2 + O_2 \rightarrow 2H_2O

. After reaction, total moles of gas (assuming water is liquid)?

Example 5

hard

CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O

16\text{ g}

CH_4

(

M=16

) and

48\text{ g}

O_2

(

M=32

) react. How many grams of excess reactant remain?

Example 6

medium

Cu + 2AgNO_3 \rightarrow Cu(NO_3)_2 + 2Ag

0.5\text{ mol}

Cu

and

0.8\text{ mol}

AgNO_3

react. Which is excess and how much remains?

Example 7

medium

2H_2 + O_2 \rightarrow 2H_2O

6\text{ mol}

H_2

and

2\text{ mol}

O_2

react. How many moles of the excess reactant remain?

Example 8

easy

N_2 + 3H_2 \rightarrow 2NH_3

1\text{ mol}

N_2

reacts with

3\text{ mol}

H_2

. With

1\text{ mol}

N_2

and

5\text{ mol}

H_2

, which is excess?

Example 9

easy

A reaction needs reactants in a

1:2

ratio. You mix

2\text{ mol}

of each. Which is in excess?

Example 10

hard

2AgNO_3 + CaCl_2 \rightarrow 2AgCl + Ca(NO_3)_2

0.6\text{ mol}

AgNO_3

and

0.4\text{ mol}

CaCl_2

react. Find excess reactant remaining.

Example 11

medium

2Ag + Cl_2 \rightarrow 2AgCl

0.4\text{ mol}

Ag

and

0.3\text{ mol}

Cl_2

react. Find the moles of excess reactant remaining.

Example 12

challenge

2KClO_3 \rightarrow 2KCl + 3O_2

... since decomposition has only one reactant, instead consider

3Mg + N_2 \rightarrow Mg_3N_2

. If

0.9\text{ mol}

Mg

and

0.4\text{ mol}

N_2

react, find excess remaining and moles of

Mg_3N_2

formed.

Example 13

easy

Mg + 2HCl \rightarrow MgCl_2 + H_2

2\text{ mol}

Mg

and

5\text{ mol}

HCl

react. Identify the excess reactant.

Example 14

easy

Zn + 2HCl \rightarrow ZnCl_2 + H_2

1\text{ mol}

Zn

reacts with

3\text{ mol}

HCl

. Which is in excess?

Example 15

hard

C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O

2\text{ mol}

C_3H_8

and

8\text{ mol}

O_2

react. How many moles of excess reactant remain?

Example 16

challenge

N_2 + 3H_2 \rightarrow 2NH_3

, after reacting

1\text{ mol}

N_2

with

4\text{ mol}

H_2

, how many total moles of gas (excess + product) are present at completion?

Example 17

medium

2Mg + O_2 \rightarrow 2MgO

6\text{ mol}

Mg

reacts with

4\text{ mol}

O_2

. How many moles of the excess reactant remain after the reaction?

Example 18

medium

5\text{ mol}

A

reacts with

5\text{ mol}

B

A + 2B \rightarrow C

, which is limiting?

Example 19

medium

2KClO_3 \rightarrow 2KCl + 3O_2

... this is a decomposition, no excess possible. Instead, for

Fe + S \rightarrow FeS

(1:1),

5\text{ mol}

Fe

and

3\text{ mol}

S

react. Excess remaining?

Example 20

hard

2Al + 6HCl \rightarrow 2AlCl_3 + 3H_2

5.4\text{ g}

Al

(

M=27

) and

0.5\text{ mol}

HCl

react. Find moles of excess reactant remaining.

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Related Concepts

Limiting Reactant Theoretical Yield