Practice 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

A starting substance that is consumed and chemically transformed during a chemical reaction, appearing on the left side of a chemical equation before the reaction.

What you start with — the ingredients that get used up to make something new.

Showing a random 20 of 50 problems.

Example 1

hard
A student writes 'water is a reactant in the dissolution of NaCl in water'. Critique this.

Example 2

easy
In an aqueous reaction, is the water solvent always a reactant?

Example 3

medium
In 2H2+O2→2H2O2H_2 + O_2 \rightarrow 2H_2O, if you start with 4 mol H2H_2 and 1 mol O2O_2, which reactant runs out first?

Example 4

medium
In CaCO3→CaO+CO2CaCO_3 \rightarrow CaO + CO_2, identify the single reactant and explain decomposition.

Example 5

easy
In CH4+2O2→CO2+2H2OCH_4 + 2O_2 \rightarrow CO_2 + 2H_2O, is oxygen a reactant or product?

Example 6

easy
Which side of the arrow do reactants appear on?

Example 7

medium
Given Pb(NO3)2(aq)+2KI(aq)→PbI2(s)+2KNO3(aq)\text{Pb(NO}_3)_2(aq) + 2\text{KI}(aq) \rightarrow \text{PbI}_2(s) + 2\text{KNO}_3(aq), list reactants and how to verify mass conservation.

Example 8

easy
In 2H2+O2→2H2O2H_2 + O_2 \rightarrow 2H_2O, name the reactants.

Example 9

easy
In the reaction Mg+2HCl→MgCl2+H2\text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2, name the reactants.

Example 10

medium
Why must you know the reactants before you can balance an equation?

Example 11

medium
A flask shows HCl(aq)+NaOH(aq)→NaCl(aq)+H2O(l)\text{HCl}(aq) + \text{NaOH}(aq) \rightarrow \text{NaCl}(aq) + \text{H}_2\text{O}(l). Which reactant is the acid?

Example 12

medium
For C2H5OH+3O2→2CO2+3H2O\text{C}_2\text{H}_5\text{OH} + 3\text{O}_2 \rightarrow 2\text{CO}_2 + 3\text{H}_2\text{O}, how many moles of O2_2 react with 0.500.50 mol ethanol?

Example 13

hard
For 2Al+3CuSO4→Al2(SO4)3+3Cu2\text{Al} + 3\text{CuSO}_4 \rightarrow \text{Al}_2(\text{SO}_4)_3 + 3\text{Cu}, 0.200.20 mol Al and 0.200.20 mol CuSO4_4 are mixed. Which reactant limits product formation?

Example 14

challenge
Two reactions share the same catalyst but different reactants. Explain how you would experimentally tell reactants from the catalyst.

Example 15

medium
In photosynthesis 6CO2+6H2O→C6H12O6+6O26\text{CO}_2 + 6\text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2, is water a reactant here?

Example 16

medium
In AgNO3(aq)+NaCl(aq)→AgCl(s)+NaNO3(aq)\text{AgNO}_3(aq) + \text{NaCl}(aq) \rightarrow \text{AgCl}(s) + \text{NaNO}_3(aq), name the reactants and the role of water.

Example 17

medium
A reaction has reactants AA and BB plus a catalyst KK. After reacting, KK is fully recovered. Which are reactants?

Example 18

easy
True or false: a substance whose mass increases during a reaction is a reactant.

Example 19

easy
Is a catalyst counted as a reactant in the net equation?

Example 20

easy
In an enzyme-catalyzed reaction, is the enzyme a reactant?
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