Reaction Predictor
Predict products with textbook rules, and look up what really happens in about 2.4 million published reactions from the Open Reaction Database. Enter names, formulas or SMILES.
About Chemical Reaction Prediction
This tool predicts the products of chemical reactions based on the type of reaction. It recognizes combustion, acid-base neutralization, synthesis (combination), decomposition, single replacement, and double replacement reactions.
Enter reactants separated by a plus sign (+). For example, CH4 + O2 for a combustion reaction or HCl + NaOH for an acid-base reaction.
Supported Reaction Types
- Combustion: A hydrocarbon reacts with oxygen to produce carbon dioxide and water. Example: CH4 + 2O2 → CO2 + 2H2O.
- Acid-Base Neutralization: An acid reacts with a base to form a salt and water. Example: HCl + NaOH → NaCl + H2O.
- Synthesis (Combination): Two or more simple substances combine to form a more complex product. Example: 2Na + Cl2 → 2NaCl.
- Decomposition: A complex substance breaks down into simpler substances. Example: 2H2O → 2H2 + O2.
- Single Replacement: One element replaces another in a compound based on the activity series. Example: Zn + CuSO4 → ZnSO4 + Cu.
- Double Replacement: Two compounds exchange ions to form two new compounds. Example: AgNO3 + NaCl → AgCl + NaNO3.
Real reactions from the Open Reaction Database
Textbook rules only go so far. Alongside them, the predictor searches about 2.4 million published reactions from the Open Reaction Database, most of them taken from US patents. Molecules are matched by structure, so a name, a formula or a SMILES string all find the same reactions. Results are grouped by product and show how often each outcome was reported, the best and typical yields, the usual temperature, the reagents, catalysts and solvents that were used, and links to the original patents and papers.
The How is it made? tab works the other way round: enter a target molecule to see the starting materials that have been used to make it. Searching for paracetamol, for example, finds the classic route from p-aminophenol and acetic anhydride.
Drug-likeness and safety checks
Any product can be assessed with the screening rules used in early drug discovery: Lipinski's rule of five, Veber's oral bioavailability rules, the QED drug-likeness score, a synthetic accessibility score, an ESOL estimate of water solubility, and structural alerts for groups that often cause trouble in assays or toxicity. Hazard information comes from the GHS classification recorded in PubChem, preferring the European Chemicals Agency summary of company notifications. These are screening estimates for learning and early triage, not measurements or safety data sheets.
How Prediction Works
The predictor analyzes the reactant formulas to identify the reaction type, then applies the corresponding rules to determine the products. For single replacement reactions, it uses the activity series of metals to determine whether a reaction will proceed. For acid-base reactions, it identifies the hydrogen-containing acid and the hydroxide-containing base to form water and the corresponding salt.
Predicted reactions are automatically balanced and displayed with the balanced equation and identified products.
Common mistakes
These are the errors that come up most often, and each one changes the answer rather than merely looking untidy.
Treating a prediction as a guarantee
Reaction prediction works from recognised patterns of reactivity. Real chemistry depends on temperature, solvent, catalyst, concentration, and time, none of which a pattern match sees. Use a prediction as a starting hypothesis to check against the literature, not as a statement of what will happen in your flask.
Ignoring reaction conditions entirely
The same two reactants can give different products under different conditions. A hydrocarbon in abundant oxygen burns to carbon dioxide and water, while the same hydrocarbon in limited oxygen produces carbon monoxide and soot. Conditions are part of the question.
Forgetting solubility rules in double replacement
A double replacement reaction only proceeds usefully if one product leaves the solution, as a precipitate, a gas, or water. If both possible products are soluble and fully dissociated, the ions simply remain mixed and no reaction has occurred.
Overlooking the activity series in single replacement
A metal will only displace another metal from a compound if it sits above it in the activity series. Copper will not displace zinc, so writing that reaction as though it proceeds produces an equation for something that does not happen.
Frequently asked questions
Which reaction types are supported?
The predictor recognises combustion, acid and base neutralisation, synthesis or combination, decomposition, and single and double replacement reactions. These cover the great majority of reactions encountered in general chemistry courses.
How reliable are the predictions?
They are reliable for the well defined reaction classes above, where products follow directly from established patterns. They are much less reliable for organic reactions with competing pathways, for anything involving catalysis, and for reactions where the outcome is governed by conditions rather than by the reactants alone.
Why did the predictor return nothing for my reactants?
Most often because the combination does not fit a recognised pattern, which frequently means no reaction occurs under ordinary conditions. It can also mean a formula was written in an unexpected way. Checking the formulas in the molar mass calculator first will rule out the second explanation.
Can it predict how fast a reaction goes?
No. Predicting products is a question about thermodynamics and reaction patterns, while reaction rate is a question about kinetics, which depends on activation energy, catalysts, and concentration. A reaction that is strongly favoured can still be immeasurably slow at room temperature.