Class 10 Science: Chemical Reactions and Equations

Comprehensive vocabulary flashcards covering key definitions, types of chemical reactions, laboratory tests, equations, and phenomena from Class 10 Chapter 1: Chemical Reactions and Equations.

Physical Change

A process in which physical properties such as state, shape, or size change without altering the chemical composition of the substance (e.g., melting of ice, melting of candle wax).

Chemical Change

A transformation in which the chemical composition of substances is altered, resulting in the creation of new substances with distinct chemical properties (e.g., combustion, rusting of iron, curdling of milk).

Chemical Reaction

A process in which one or more starting substances undergo chemical transformation to produce one or more completely new substances.

Chemical Equation

The symbolic representation of a chemical reaction using the chemical formulas of the reactants and products.

Reactants

The starting chemical substances written on the left-hand side of a chemical equation that undergo transformation during the reaction.

Products

The new chemical substances formed on the right-hand side of a chemical equation as a result of a chemical reaction.

Law of Conservation of Mass

A fundamental principle stating that mass can neither be created nor destroyed in a chemical reaction; thus, the total number of atoms of each element must remain equal on both sides of a balanced equation.

Aqueous State ($aq$)

A notation indicating that a chemical compound or reactant is dissolved in water to form a solution.

Exothermic Reaction

A chemical reaction that releases energy to the surroundings, primarily in the form of heat (e.g., respiration, burning of natural gas, reaction of quick lime with water).

Endothermic Reaction

A chemical reaction that absorbs energy from its surroundings to proceed (e.g., photosynthesis, thermal decomposition reactions).

Precipitate

An insoluble solid substance that separates and settles out of an aqueous solution during a chemical reaction.

Catalyst

A substance that speeds up or slows down the rate of a chemical reaction without itself being consumed or permanently altered in the process.

Combination Reaction

A reaction in which two or more reactants join together to form a single new product.

Magnesium Ribbon Reaction

The burning of cleaned magnesium ribbon in air with a dazzling white flame to form a white powder consisting of magnesium oxide ($2Mg + O_2 \rightarrow 2MgO$).

Quick Lime

The common name for calcium oxide ($CaO$), an inorganic compound used in cement manufacturing that reacts vigorously with water in an exothermic reaction to yield slaked lime.

Slaked Lime

The common name for calcium hydroxide ($Ca(OH)_2$), formed by mixing quick lime with water; it is applied to walls during whitewashing and reacts with atmospheric $CO_2$ to give a shiny finish.

Lime Water Test

A standard qualitative test for carbon dioxide gas ($CO_2$) where bubbling the gas through dilute slaked lime solution turns it milky due to the formation of insoluble calcium carbonate ($CaCO_3$).

Decomposition Reaction

A type of chemical reaction where a single reactant breaks down into two or more simpler products upon the addition of energy in the form of heat, light, or electricity.

Thermal Decomposition (Thermolysis)

A decomposition reaction that occurs when heat energy is supplied to break down a chemical compound.

Ferrous Sulphate Decomposition

The thermal breakdown of pale green $FeSO_4 \cdot 7H_2O$ crystals, which lose water of crystallization to turn white, and further decompose into reddish-brown ferric oxide ($Fe_2O_3$) and acidic gases ($SO_2$ and $SO_3$).

Lead Nitrate Decomposition

The thermal decomposition of colorless lead nitrate ($Pb(NO_3)_2$) into a yellow solid of lead oxide ($PbO$), pungent brown fumes of nitrogen dioxide ($NO_2$), and colorless oxygen gas ($O_2$).

Electrolytic Decomposition (Electrolysis)

A decomposition process driven by passing an electric current through a liquid or solution, such as decomposing acidified water into hydrogen at the cathode and oxygen at the anode in a $2:1$ ratio by volume.

Pop Sound Test

A diagnostic confirmatory test for hydrogen gas ($H_2$), in which bringing a lit candle or flame near the gas produces a distinctive popping sound.

Photolytic Decomposition (Photolysis)

A decomposition reaction that is triggered and driven by the absorption of light photons (sunlight).

Silver Chloride Photolysis

The photochemical decomposition of white silver chloride ($AgCl$) into grey elemental silver ($Ag$) and chlorine gas ($Cl_2$) when exposed to sunlight; historically used in black-and-white photography.

Displacement Reaction

A chemical reaction in which a more chemically active element displaces a less active element from its compound or salt solution.

Reactivity Series

A ranked series of metals arranged in decreasing order of their chemical reactivity, allowing prediction of single displacement reactions.

Iron-Copper Sulphate Displacement

A reaction where iron nails placed in a blue copper sulphate ($CuSO_4$) solution displace copper, changing the solution color to light green ($FeSO_4$) and coating the nails with brown copper.

Double Displacement Reaction

A reaction in which two reacting chemical compounds exchange their corresponding ions to create two entirely new compounds.

Precipitation Reaction

A chemical reaction (commonly double displacement) between two soluble salt solutions that produces an insoluble solid known as a precipitate.

Lead Iodide Precipitation

A double displacement reaction occurring between colorless aqueous solutions of lead nitrate and potassium iodide, yielding a bright yellow precipitate of lead iodide ($PbI_2$).

Barium Sulphate Precipitation

A double displacement reaction between sodium sulphate ($Na_2SO_4$) and barium chloride ($BaCl_2$) that yields an insoluble white precipitate of barium sulphate ($BaSO_4$).

Oxidation

A chemical process characterized by the gain of oxygen atoms or the loss/removal of hydrogen atoms from a substance.

Reduction

A chemical process characterized by the loss/removal of oxygen atoms or the addition/gain of hydrogen atoms to a substance.

Redox Reaction

A chemical reaction in which both oxidation and reduction processes occur simultaneously across the participating species.

Oxidizing Agent (Oxidant)

A substance that facilitates oxidation by donating oxygen or accepting hydrogen, and consequently undergoes reduction itself during the reaction.

Reducing Agent (Reductant)

A substance that facilitates reduction by supplying hydrogen or removing oxygen, and consequently undergoes oxidation itself during the reaction.

Copper Oxidation and Reduction

The reaction where brown metallic copper oxidizes to form black copper(II) oxide ($CuO$) upon heating in air, which can be reversed back to reddish-brown copper by passing hydrogen gas over it.

Corrosion

The gradual destruction and deterioration of a metal surface through chemical action caused by environmental agents such as moisture, oxygen, or acids.

Rusting of Iron

A specific form of corrosion where iron reacts with both air (oxygen) and water/moisture simultaneously, resulting in a reddish-brown flaky substance called hydrated iron oxide.

Tarnishing of Silver

The corrosion phenomenon in which shiny silver reacts with atmospheric sulphur compounds over time to form a dull black coating of silver sulphide.

Rancidity

The process of slow aerial oxidation of fats and oils present in food items, producing an unpleasant odor and spoiled taste.

Antioxidants

Chemical substances added to fat- and oil-containing foods to prevent or slow down oxidation, thereby protecting the food from turning rancid.