Complete a chemical reaction: predict the products and balance

Enter the reactants separated by «+». The calculator predicts the products by the rules of school inorganic chemistry, balances the equation and shows the precipitate or gas, the reaction type and the ionic equations. If no reaction occurs or the case is outside the school rules, it says so.

Reactants

Read as: Zn + HCl

Type formulas as plain text: H2SO4, Ca(OH)2, CuSO4·5H2O. Case matters: Co is cobalt, CO is carbon monoxide. Mark a concentrated acid: H2SO4(conc). A single substance means thermal decomposition. If you know the products, add them after «=» and the equation will just be balanced.

Answer

Zn + 2HCl → ZnCl₂ + H₂↑

Products: ZnCl₂; H₂↑ — gas
Reaction type: single displacement
Rule: A metal above hydrogen in the activity series displaces hydrogen from an acid: metal + acid → salt + H₂↑.

Ionic equations

Complete: Zn + 2H⁺ + 2Cl⁻ → Zn²⁺ + 2Cl⁻ + H₂↑

Net: Zn + 2H⁺ → Zn²⁺ + H₂↑

Solution

Zn is a metal.
HCl is an acid.
Zn is above hydrogen in the activity series and displaces hydrogen from the acid.
Formula from charges: Zn²⁺ and Cl⁻, LCM of charges = 2 → ZnCl₂.
Balance the equation (the same number of atoms of each element on both sides): Zn + 2HCl → ZnCl₂ + H₂↑.

Solubility table

S — soluble, sS — slightly soluble, I — insoluble, «—» — decomposes in water or does not exist. Hover over a cell to see the formula. The data follow the school solubility table; the calculator uses the same data to decide whether a precipitate forms.

	H⁺	Li⁺	K⁺	Na⁺	NH₄⁺	Ba²⁺	Ca²⁺	Mg²⁺	Sr²⁺	Al³⁺	Cr³⁺	Fe²⁺	Fe³⁺	Ni²⁺	Co²⁺	Mn²⁺	Zn²⁺	Ag⁺	Hg²⁺	Pb²⁺	Sn²⁺	Cu²⁺
OH⁻		S	S	S	S	S	sS	I	sS	I	I	I	I	I	I	I	I	—	—	I	I	I
Cl⁻	S	S	S	S	S	S	S	S	S	S	S	S	S	S	S	S	S	I	S	sS	S	S
Br⁻	S	S	S	S	S	S	S	S	S	S	S	S	S	S	S	S	S	I	sS?	sS	S	S
I⁻	S	S	S	S	S	S	S	S	S	S	S?	S	—	S	S	S	S	I	I	I	sS?	—
S²⁻	S	S	S	S	S	S?	sS?	S?	S?	—	—	I	—?	I	I	I	I	I	I	I	I	I
SO₃²⁻	S	S	S	S	S	I	I	sS?	I	—	—	I?	—?	I?	I?	I?	I?	I	—?	I	—?	—?
SO₄²⁻	S	S	S	S	S	I	sS	S	I	S	S	S	S	S	S	S	S	sS	—?	I	S	S
NO₃⁻	S	S	S	S	S	S	S	S	S	S	S	S	S	S	S	S	S	S	S	S	—?	S
PO₄³⁻	S	I?	S	S	S	I	I	I	I	I	I	I	I	I	I	I	I	I	I	I	I	I
CO₃²⁻	S	S	S	S	S	I	I	I?	I	—	—	I	—	I	I	I	I	I	—?	I	—?	—?
SiO₃²⁻	I	S	S	S	—?	I	I	I	I	—?	—?	I	—?	I?	I?	I	I	—?	—?	I	—?	—?

«?» marks cells on which school sources disagree or the compound hydrolyses noticeably (sulfides of Ca, Mg, Sr, Ba; sulfites and silicates of several metals; HgSO₄, Sn(NO₃)₂, SnI₂, CrI₃, HgBr₂, Li₃PO₄, MgCO₃ and others). The calculator gives no answer when a reaction depends on such a cell. Fluorides and acetates are not included yet.

How to predict the products of a reaction

Products are not guessed: they follow from the classes of the reactants. First decide what each reactant is: a metal, a non-metal, an oxide (basic, amphoteric, acidic), a base, an acid or a salt. Then one of the rules applies.

Main school rules

Acid + base → salt + water (neutralisation): NaOH + HCl → NaCl + H₂O.
Metal + acid → salt + hydrogen if the metal is above hydrogen in the activity series: Zn + 2HCl → ZnCl₂ + H₂↑. Copper, silver and gold do not react with hydrochloric or dilute sulfuric acid. Nitric and concentrated sulfuric acids are oxidising acids and do not release hydrogen.
Metal + salt → new salt + new metal if the metal is more reactive than the metal in the salt: Fe + CuSO₄ → FeSO₄ + Cu. Iron forms iron(II) salts here.
Double displacement between salts, a salt and an acid, a salt and an alkali goes to completion only if a precipitate, a gas or water forms. Precipitates are found from the solubility table: BaCl₂ + Na₂SO₄ → BaSO₄↓ + 2NaCl. Gases come from unstable acids: carbonic (CO₂↑ + H₂O), sulfurous (SO₂↑), hydrosulfuric (H₂S↑), and from ammonium salts with an alkali (NH₃↑).
Oxides: basic oxide + acid → salt + water; acidic oxide + alkali → salt + water; basic + acidic oxide → salt. Oxides of alkali and alkaline-earth metals react with water to give alkalis; acidic oxides except SiO₂ give acids.
Combustion: element + O₂ → oxide; hydrocarbon + O₂ → CO₂ + H₂O.
Thermal decomposition: insoluble base → oxide + water; carbonate (except Na₂CO₃, K₂CO₃) → oxide + CO₂.

Writing the formula of a product

A salt formula is built from the ion charges so that the total charge is zero. For Fe³⁺ and SO₄²⁻ the least common multiple of the charges is 6, so there are 6 / 3 = 2 iron ions and 6 / 2 = 3 sulfate ions: Fe₂(SO₄)₃. The calculator shows this step for every salt.

Ionic equations

In the complete ionic equation strong electrolytes are written as ions: soluble salts, alkalis and strong acids (HCl, HBr, HI, HNO₃, H₂SO₄). Precipitates, gases, water, weak acids and oxides stay as molecules. Cancelling the spectator ions gives the net ionic equation.

What the calculator does not do

It does not predict redox reactions with HNO₃, concentrated H₂SO₄, KMnO₄, K₂Cr₂O₇, amphoteric substances with alkalis, hydrolysis or organic reactions other than combustion. Their products depend on conditions, and we will not guess them: enter the products yourself and the calculator will balance the equation. Solubility table cells on which school sources disagree are marked «?», and no answer is given when the result depends on them.

FAQ

How do I know whether a double displacement reaction occurs?

It goes to completion if a precipitate forms (see the solubility table), a gas is released (CO₂, SO₂, H₂S, NH₃) or water forms. If all the products are soluble, the ions simply stay in solution and there is no reaction, as with KNO₃ + NaCl.

Why doesn't copper react with hydrochloric acid?

Copper is below hydrogen in the activity series, so it cannot displace hydrogen from acids. Copper does react with nitric and concentrated sulfuric acid, but no hydrogen is formed: these are redox reactions whose products depend on concentration.

Why does iron give FeCl₂ and not FeCl₃?

Hydrogen ions in hydrochloric and dilute sulfuric acid are a weak oxidising agent and oxidise iron only to +2. Chlorine is a strong oxidising agent, so iron burning in chlorine gives FeCl₃.

What does «the calculator does not predict this case» mean?

These are reactions whose products depend on concentration, temperature or an excess of a reactant: nitric and concentrated sulfuric acid, permanganate, dichromate, amphoteric hydroxides in alkali, hydrolysis, organic chemistry. We decline rather than guess. If you know the products, add them after «=» and the equation will be balanced.

How do I type a charge, a hydrate or a concentrated acid?

Charge with ^: SO4^2-, Fe^3+ (Na+ and Cl- also work). A hydrate with a dot or an asterisk: CuSO4·5H2O, CuSO4*5H2O. A concentrated acid in brackets: H2SO4(conc). No need to type subscripts: digits after an element symbol become subscripts automatically.