⚗️Chemistry200 事実

Reactions & Compounds

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A chemical compound is formed when two or more elements bond together.
Water is a compound made of two hydrogen atoms and one oxygen atom.
A chemical reaction rearranges atoms to form new substances.
In a covalent bond, atoms share pairs of electrons.
In an ionic bond, electrons are transferred between atoms.
Acids release hydrogen ions when dissolved in water.
Bases accept hydrogen ions and often feel slippery to the touch.
The pH scale measures how acidic or basic a solution is.
A neutral solution like pure water has a pH of seven.
Combustion is a reaction in which a fuel burns in oxygen.
A catalyst speeds up a reaction without being consumed by it.
Salt is an ionic compound made of sodium and chlorine.
Photosynthesis converts carbon dioxide and water into glucose and oxygen.
The law of conservation of mass states matter is neither created nor destroyed.
Mixtures can be separated by physical means like filtration or distillation.
Carbon dioxide is produced when fossil fuels are burned.
A synthesis reaction combines two or more reactants into a single product.
A decomposition reaction breaks one compound into two or more simpler substances.
In a single displacement reaction, one element replaces another in a compound.
In a double displacement reaction, two compounds exchange their ions.
Endothermic reactions absorb energy from their surroundings as they proceed.
Exothermic reactions release energy, usually as heat, to their surroundings.
Balancing an equation ensures equal numbers of each atom on both sides.
Coefficients in an equation show the relative amounts of substances reacting.
The mole is the SI unit for the amount of a substance.
One mole contains about 6.022 times ten to the twenty-third particles.
Avogadro's number defines the count of particles in one mole.
Molar mass is the mass in grams of one mole of a substance.
Stoichiometry uses mole ratios to relate amounts of reactants and products.
A limiting reactant is fully consumed and determines the maximum product yield.
An excess reactant remains after a reaction reaches completion.
Percent yield compares actual product obtained to the theoretical maximum amount.
Oxidation involves the loss of electrons by an atom or ion.
Reduction involves the gain of electrons by an atom or ion.
A redox reaction couples oxidation and reduction occurring together.
An oxidizing agent gains electrons and is itself reduced in a reaction.
A reducing agent loses electrons and is itself oxidized in a reaction.
Oxidation states help track electron transfer during chemical reactions.
Rusting is the slow oxidation of iron in the presence of oxygen.
Corrosion is the gradual degradation of metals by chemical reactions.
Galvanizing coats iron with zinc to protect it from corrosion.
Electrolysis uses electric current to drive a non-spontaneous chemical reaction.
Electroplating deposits a thin metal layer using an electric current.
A galvanic cell converts chemical energy into electrical energy spontaneously.
Batteries store and release energy through controlled electrochemical reactions inside them.
The activation energy is the minimum energy needed to start a reaction.
Catalysts work by lowering the activation energy of a reaction.
Enzymes are biological catalysts that speed up reactions in living cells.
Increasing temperature generally increases the rate of a chemical reaction.
Higher reactant concentration usually increases the rate of a reaction.
Collision theory states reactions occur when particles collide with enough energy.
At equilibrium, the concentrations of reactants and products remain constant.
Le Chatelier's principle predicts how equilibrium shifts under applied stress.
Adding reactant shifts an equilibrium toward forming more product.
Reversible reactions can proceed in both forward and backward directions.
An irreversible reaction proceeds essentially in only one direction.
A precipitate is an insoluble solid formed during a reaction in solution.
A precipitation reaction produces an insoluble product from soluble reactants.
Neutralization is the reaction between an acid and a base.
Acid-base neutralization typically produces a salt and water.
Hydrochloric acid reacts with sodium hydroxide to form salt and water.
A strong acid dissociates almost completely in aqueous solution.
A weak acid only partially dissociates in aqueous solution.
Sulfuric acid is a strong diprotic acid used widely in industry.
Nitric acid is a strong acid used to make fertilizers and explosives.
Acetic acid is the weak acid that gives vinegar its sour taste.
Sodium hydroxide is a strong base also known as caustic soda.
Ammonia is a weak base with the chemical formula NH3.
Calcium hydroxide, called slaked lime, forms a basic solution in water.
An indicator changes color depending on the pH of a solution.
Litmus paper turns red in acids and blue in bases.
Phenolphthalein is colorless in acid and pink in basic solutions.
The pH scale typically ranges from zero to fourteen.
A pH below seven indicates an acidic solution.
A pH above seven indicates a basic or alkaline solution.
A buffer resists changes in pH when small amounts of acid are added.
Titration determines an unknown concentration using a solution of known concentration.
The equivalence point in a titration occurs at complete neutralization.
Hydrogen gas burns in oxygen to form water vapor.
Methane burns in oxygen to produce carbon dioxide and water.
Complete combustion of hydrocarbons yields carbon dioxide and water.
Incomplete combustion can produce toxic carbon monoxide gas.
Carbon monoxide is a colorless, odorless, and poisonous gas.
Oxygen normally exists as a diatomic molecule with formula O2.
Nitrogen makes up about seventy-eight percent of Earth's atmosphere.
Ozone is a molecule made of three oxygen atoms.
The ozone layer absorbs much of the Sun's ultraviolet radiation.
A metallic bond involves a sea of delocalized electrons among metal ions.
Metals conduct electricity because of their freely moving electrons.
Alloys are mixtures of metals or a metal with other elements.
Steel is an alloy of iron and carbon.
Bronze is an alloy of copper and tin.
Brass is an alloy of copper and zinc.
A hydrogen bond is a weak attraction between molecules containing hydrogen.
Hydrogen bonding gives water many of its unusual properties.
Polar molecules have an uneven distribution of electric charge.
Nonpolar molecules have an even distribution of electric charge.
Water is a polar solvent that dissolves many ionic compounds.
Like dissolves like means polar solvents dissolve polar solutes.
A solute is the substance dissolved in a solution.
A solvent is the substance that dissolves the solute.
Molarity expresses concentration as moles of solute per liter of solution.
A saturated solution holds the maximum dissolvable solute at a given temperature.
A supersaturated solution holds more solute than normally possible.
Solubility describes how much solute can dissolve in a solvent.
Most solids become more soluble in water as temperature increases.
Gases generally become less soluble in water as temperature increases.
A suspension contains particles large enough to settle out over time.
A colloid contains particles dispersed but not dissolved in a medium.
Milk is an everyday example of a colloid dispersed in water.
An emulsion is a colloid of two immiscible liquids.
Chromatography separates mixtures based on differing component movement rates.
Distillation separates liquids based on differences in their boiling points.
Filtration separates insoluble solids from liquids using a porous barrier.
Evaporation can recover a dissolved solid from its solution.
Crystallization forms pure solid crystals from a solution.
An element is a substance that cannot be broken down chemically.
A compound has fixed proportions of its constituent elements by mass.
The law of definite proportions states compounds have constant composition.
An empirical formula shows the simplest whole-number ratio of atoms.
A molecular formula shows the actual number of atoms in a molecule.
Glucose has the molecular formula C6H12O6 and is a simple sugar.
Carbon dioxide consists of one carbon and two oxygen atoms.
Sodium chloride forms a cubic crystal lattice of alternating ions.
A cation is a positively charged ion formed by losing electrons.
An anion is a negatively charged ion formed by gaining electrons.
Ions form when atoms gain or lose electrons.
A polyatomic ion is a charged group of covalently bonded atoms.
The sulfate ion has the formula SO4 with a two-minus charge.
The nitrate ion has the formula NO3 with a one-minus charge.
The ammonium ion has the formula NH4 with a one-plus charge.
The carbonate ion has the formula CO3 with a two-minus charge.
The hydroxide ion has the formula OH with a one-minus charge.
Calcium carbonate is the main component of limestone and chalk.
Baking soda is the common name for sodium bicarbonate.
Baking soda releases carbon dioxide when it reacts with acid.
Hydrogen peroxide decomposes into water and oxygen gas.
Antoine Lavoisier is regarded as a founder of modern chemistry.
Lavoisier helped establish the law of conservation of mass.
John Dalton proposed an early atomic theory of matter in the 1800s.
Dmitri Mendeleev arranged elements into the first widely accepted periodic table.
Mendeleev's periodic table predicted properties of then-undiscovered elements.
Svante Arrhenius proposed a theory of acids and bases involving ions.
The Arrhenius definition describes acids as substances that produce hydrogen ions.
The Bronsted-Lowry theory defines acids as proton donors.
The Bronsted-Lowry theory defines bases as proton acceptors.
The Lewis theory defines acids as electron-pair acceptors.
The Lewis theory defines bases as electron-pair donors.
Fritz Haber developed a process for synthesizing ammonia from nitrogen.
The Haber process combines nitrogen and hydrogen to make ammonia.
The Haber process requires high pressure, moderate heat, and an iron catalyst.
Ammonia produced industrially is used mainly to make fertilizers.
The contact process is used to manufacture sulfuric acid industrially.
Joseph Priestley is credited with discovering oxygen gas.
Linus Pauling made major contributions to understanding chemical bonding.
Electronegativity measures an atom's tendency to attract bonding electrons.
Fluorine is the most electronegative of all the chemical elements.
A nonpolar covalent bond forms between atoms of equal electronegativity.
A polar covalent bond forms between atoms of different electronegativity.
Valence electrons are the outermost electrons involved in bonding.
The octet rule states atoms tend to gain eight valence electrons.
Noble gases are generally unreactive due to full electron shells.
Helium, neon, and argon are examples of noble gases.
A Lewis structure shows the arrangement of valence electrons in a molecule.
A double bond involves two shared pairs of electrons.
A triple bond involves three shared pairs of electrons.
Nitrogen gas contains a strong triple bond between two atoms.
Carbon can form four covalent bonds with other atoms.
Organic chemistry is the study of carbon-containing compounds.
Methane is the simplest hydrocarbon, with one carbon atom.
Alkanes are hydrocarbons with only single carbon-carbon bonds.
Alkenes are hydrocarbons containing at least one carbon-carbon double bond.
Alkynes are hydrocarbons containing at least one carbon-carbon triple bond.
Ethanol is the type of alcohol found in alcoholic beverages.
A polymer is a large molecule built from repeating smaller units.
Polymerization joins many small monomers into a long polymer chain.
Polyethylene is a common plastic made from ethylene monomers.
Proteins are natural polymers built from amino acid units.
Cellulose is a natural polymer found in plant cell walls.
Fermentation converts sugars into alcohol and carbon dioxide.
Respiration releases energy by breaking down glucose with oxygen.
Cellular respiration is essentially the reverse of photosynthesis.
A thermal decomposition reaction uses heat to break down a compound.
Heating calcium carbonate produces calcium oxide and carbon dioxide.
Calcium oxide is commonly known as quicklime and reacts with water.
More reactive metals can displace less reactive metals from solutions.
Potassium and sodium are highly reactive alkali metals.
Gold and platinum are very unreactive precious metals.
Halogens are highly reactive nonmetals in group seventeen.
Chlorine is a greenish-yellow halogen gas used to disinfect water.
A spectator ion appears unchanged on both sides of a reaction.
Hard water contains dissolved calcium and magnesium ions.
The branch studying energy changes in reactions is called thermodynamics.
Enthalpy is a measure of the heat content of a system.
Anhydrous copper sulfate is white but turns blue when hydrated.
Water of crystallization is water chemically bound within a crystal.
Sublimation is the direct change from solid to gas without melting.
Dry ice is solid carbon dioxide that sublimes at room temperature.
A chemical change produces new substances with different properties.
A physical change alters form without producing new substances.

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