science

Trihalomethane

Trihalomethane is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Trihalomethane rather than just read about it. In short: In chemistry, trihalomethanes (THMs) are chemical compounds in which three of the four hydrogen atoms of methane (CH4) are replaced by halogen atoms. Trihalomethanes with all the same halogen atoms are called haloforms.

Key takeaways

Trihalomethane belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Trihalomethane to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Trihalomethane from memory before moving on to harder problems.

Reference excerpt

In chemistry, trihalomethanes (THMs) are chemical compounds in which three of the four hydrogen atoms of methane (CH4) are replaced by halogen atoms. Trihalomethanes with all the same halogen atoms are called haloforms. Many trihalomethanes find uses in industry as solvents or refrigerants. Some THMs are also environmental pollutants, and a few are considered carcinogenic.

Table of common trihalomethanes

Industrial uses Only chloroform has significant applications of the haloforms. In the predominant application, chloroform is required for the production of tetrafluoroethylene (TFE), precursor to teflon. Chloroform is fluorinated by reaction with hydrogen fluoride to produce chlorodifluoromethane (R-22). Pyrolysis of chlorodifluoromethane (at 550–750 °C) yields TFE, with difluorocarbene as an intermediate.

CHCl 3 + 2 HF ⟶ CHClF 2 + 2 HCl {\displaystyle {\ce {CHCl3 + 2 HF -> CHClF2 + 2 HCl}}}

2 CHClF 2 ⟶ C 2 F 4 + 2 HCl {\displaystyle {\ce {2 CHClF2 -> C2F4 + 2 HCl}}}

Refrigerants and solvents Trihalomethanes released to the environment break down faster than chlorofluorocarbons (CFCs), thereby doing much less damage to the ozone layer. Trifluoromethane and chlorodifluoromethane are both used as refrigerants. Chlorodifluoromethane is a refrigerant HCFC, or hydrochlorofluorocarbon, while fluoroform is an HFC, or hydrofluorocarbon. Fluoroform is not ozone depleting. Chloroform is a common solvent in organic chemistry.

Occurrence and production The total global flux of chloroform through the environment is approximately 660000 tonnes per year, and about 90% of emissions are natural in origin. Many kinds of seaweed produce chloroform, and fungi are believed to produce chloroform in soil. Most of the haloforms — specifically, chloroform (CHCl3), bromoform (CHBr3), and iodoform (CHI3) — are easy to prepare through the haloform reaction, although this method does not lend itself to bulk syntheses. (Fluoroform (CHF3) cannot be prepared in this manner.) Chloroform is produced by heating mixtures of methane or methyl chloride with chlorine. Dichloromethane is a coproduct. Bromochlorofluoromethane is one of the simplest possible stable chiral compounds, and is used for studies.

Regulation Trihalomethanes were the subject of the first drinking water regulations issued after passage of the U.S. Safe Drinking Water Act in 1974. The EPA limits the total concentration of the four chief constituents (chloroform, bromoform, bromodichloromethane, and dibromochloromethane), referred to as total trihalomethanes (TTHM), to 80 parts per billion in treated water. Traces of chloroform are produced in swimming pools.

References

External links National Pollutant Inventory - Chloroform and trichloromethane How Ozone Technology Reduces Disinfection Byproducts EPA - Trihalomethanes in Drinking Water: Sampling, Analysis, Monitoring and Compliance (August 1983)

Worked examples

Example 1 — a first encounter with Trihalomethane

Start with the simplest possible case. Write down what Trihalomethane claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Trihalomethane before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Trihalomethane ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Trihalomethane

In research: Trihalomethane appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Trihalomethane in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Trihalomethane is common in secondary-school and first-year university syllabi. It links to neighbouring topics Halogenated solvents, Halomethanes, Refrigerants, so understanding it makes those chapters shorter.
In everyday life: Look for Trihalomethane outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Trihalomethane in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Trihalomethane means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Trihalomethane out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Trihalomethane in simple terms?

Why does Trihalomethane matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Trihalomethane?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Trihalomethane.