Chemical Reaction And Equations

Made By:- Pranav Ghildiyal

and Ratik Class :- ‘X’ D

Introduction to chemical reactions• A chemical reaction is what really happens. For example, when magnesium burns, a shiny, lustrous piece of flexible metallic ribbon is heated in the presence of a colourless, transparent gas and changes into a white-to-grey, opaque, crumbly, powdery solid. That is a chemical reaction.

• When water is electrolyzed, we can write that H2O becomes H2 and O2. "H2O H2 + O2" is an equation that represents the reaction. The reaction itself is the formation of two colourless gases, hydrogen and oxygen, when an electric current is passed through the colourless transparent liquid, water. It is Important that you realize the distinction between reactions and equations.

• The term "reactant" is the same as the term "reagent." It refers to each of the chemicals that are reacting with one another; in other words, what you have when you start the reaction. The chemicals that you get as the reaction proceeds are called the "products." So, as a chemical reaction proceeds, you start with reactants and you end up with products. When magnesium burns, you have magnesium and oxygen as the reactant . The magnesium oxide is the product.

Introduction to chemical equations• A chemical reaction equation is a symbolic notation system for describing chemical changes. Reactants are the substances that are present before the chemical change. These are written on the left side of the reaction equation. The products are the substances that are present after the chemical change. These are written on the right side of the reaction equation. An arrow (à) separates the reactants and the products. An equilibrium is a chemical reaction in which the reactants are converted into products at the same time and rate that the products are converted into reactants. The reaction arrow for an equilibrium looks like right and left pointing arrows written one on top of the other.

• Information about the state (solid, liquid, gas) or solution (aqueous, precipitate) is written in parenthesis after the chemical formula.

• Coefficients are the relative number of moles of each of the reactants and products. These numbers are written in front of the chemical formulas. In the reaction equation below, the coefficients indicate that there are two moles of sodium hydroxide and water for every one mole of sulfuric acid and sodium sulphate.2NaOH(aq) + H2SO4(aq) à Na2SO4(aq) + 2H2O(l)

Parts of chemical equationsreactants

• Reactants (or 'substrates') are two or more elements/ compounds that chemically interact to form a new substance. They are the starting materials for a reaction and are always found at the left side of a chemical equations.

products

• Product(s) are formed during chemical reactions Products have lower energy than the reagents and are produced during the reaction. Products are formed as the chemical reaction progresses toward chemical equilibrium at a certain reaction rate, which depends on the reagents and environmental conditions.

Symbols Of Physical State

• Gaseous • Liquid • Aqueous • Solid

(g)(l)(aq)(s)

Balancing chemical equations

Step 1 :- Take an unbalanced equation.

Step 2 :- Draw boxes around all the chemical formulas.

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Balancing chemical equationsStep 3 :- Make an element inventory.

Step 4 :- Write numbers in front of each of the boxes until the inventory for each element is the same both before and after the reaction.

Step 5 :- Now the equation is balanced

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Exothermic reaction• An exothermic reaction is a chemical reaction that is accompanied by the release of heat. In other words, the energy needed for the reaction to occur is less than the total energy released. As a result of this, the extra energy is released, usually in the form of heat. Where an exothermic reaction causes heating of the reaction vessel which is not controlled, the rate of reaction can increase, in turn causing heat to be evolved even more quickly . This positive feedback situation is known as thermal runaway. An explosion can also result from the problem. Heat production or absorption in either a physical process or chemical reaction is measured using calorimetry. One common Laboratory instrument is the reaction calorimeter, where the heat flow into or from the reaction vessel is monitored. The technique can be used to follow chemical reactions as well as physical processes such as crystallisation and dissolution.

Examples of Exothermic reaction• Breathing• White washing• Combustion reactions of fuels• Neutralization reactions such as direct reaction of acid and

base• Adding concentrated acid to water• Burning of a substance• Adding water to anhydrous copper(II) sulphate• Reactions taking place in a self-heating can based on lime and

aluminium• The setting of cement and concrete• Many corrosion reactions such as oxidation of metals• Most polymerisation reactions• The Haber-Bosch process of ammonia production

Endothermic reaction• An endothermic reaction is a chemical reaction in which energy is absorbed from the surrounding environment in place of being released as it is in the exothermic reaction. It is also called as a hypothermic reaction. Heat is compulsory for this reaction as it is absorbed during the reaction takes place.

• Examples:-

• melting ice cubes• melting solid salts• evaporating liquid water• converting frost to water vapour (melting, boiling, and evaporation in

general are endothermic processes)• making an anhydrous salt from a hydrate• splitting a gas molecule• reacting ethanoic acid with sodium carbonate• photosynthesis (chlorophyll is used to react carbon dioxide plus water

plus energy to make glucose and oxygen)

Types of chemical reactions

• Combination Reaction• Decomposition Reaction• Displacement Reaction• Double Displacement Reaction

Combination Reaction• A combination reaction or a synthesis reaction is a general category of a chemical reaction (the term usually refers to an inorganic chemical reaction), in which two or more reactants are chemically bonded together to produce a single product. When two or more substances combine to form a single product, it is known as a combination reaction. Many elements react with one another in this fashion to form compounds.

• This reaction is usually exothermic because when the bond forms between the elements, heat is released. Combination reaction has two or more reactants and one product formed by it. When a combination reaction occurs between a metal and a non-metal the product is an ionic solid. An example could be Lithium + Sulphur →Lithium Sulphide

A + B = C• A combination reaction can be of three types:Type Example

a) Between two elements C + O2 → CO2

b) Between two compounds CaO + H2O → Ca(OH)2

c) Between an element and a compound O + H2O → H2O2

Decomposition Reaction• A decomposition reaction is a type of chemical reaction in which a substance degrades into two or more basic components. It is a process in direct contrast to that of chemical synthesis, which involves molecular bonding so that two or more components may join to form a single chemical compound. The decomposition reaction often requires exposure to a catalyst, such as a heat source or solvent. A simple example of such a breakdown is the conversion of water (H2O) into hydrogen (H2) and oxygen (O2) gas via a process known as the electrolysis of water.

• Decomposition chemical reactions are generally classified into three main types, which are catalytic, electrolytic, or thermal. In catalytic reactions, an agent is introduced to cause a chemical reaction. For example, hydrogen peroxide readily degrades into water and oxygen in the presence of manganese dioxide. An electrolytic decomposition reaction is achieved by exposing an aqueous solution or molten compound to an electrical current. Thermal decomposition occurs when a compound is affected by direct heat or radiation.

C = A+ B

2HgO (s) → 2Hg (l) + O2 (g)

2Cl2O5 (g) → 2Cl2 (g) + 5O2 (g)

2N2O5 (g) → O2 (g) + 4NO2 (g)

Mg(NO3)2 (s) → Mg(NO2)2 (s) + O2 (g)

2SO3 (g) → 2SO2 (g) + O2 (g)

Displacement Reaction• Displacement reactions are the reactions in which a more reactive element displaces a lesser reactive Element from it’s compound is known as displacement reaction.

• These reactions are generally found to occur in solutions. The elements involved may be metals, non-metals, i.e., a more reactive metal may displace a lesser reactive metal or a more reactive non-metal may displace a lesser reactive non-metal.

Examples :-

1. Mg + 2 H2O ---> Mg(OH)2 + H2

2. 2 KI + Cl2 ---> 2 KCl + I2

Double Displacement Reaction• The reaction in which two compounds react by an exchange of ions to form two new compounds .a double displacement reaction usually occurs in solution and one of the products ,being insoluble precipitates out.

let us take an example in which we will mix the solutions of sodium chloride and silver nitrate will precipitate out white silver chloride. nitrate ions and chloride ions have been exchanged in this reaction.

AB + CD --> AC + BD

Examples :-

• AgNO3+naCl----->AgCl+NaNO3• Pb(NO3)2 (aq) + 2KCl(aq) -> PbCl2 (s) +2KNO3(s)• NaCl + KBr -> NaBr + KCl• Lead Nitrate and Potassium Iodide• Sodium Chloride and Silver Nitrate

Oxidation and Reduction - Redox Reaction• An oxidation-reduction reaction (redox reaction) is a reaction in which electrons are transferred between species or in which atoms change oxidation numbers. Oxidation is the portion of the redox reaction in which there is a loss of electrons by a species or an increase in the oxidation number of an atom. Reduction is the part of a reaction in which there is a gain of electrons by a species or a decrease in the oxidation number of an atom. Something that is oxidized loses electrons or contains an atom that increases in oxidation number. Something that is reduced gains electrons or has an atom that decreases in oxidation number. An oxidizing agent is a something that oxidizes something, meaning that the oxidation agent is itself reduced. A reducing agent is a something that reduces something else, and is itself oxidized.

Oxidation and Reduction - Redox Reaction

Corrosion • Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen. Formation of an oxide of iron due to oxidation of the iron atoms in solid solution is a well-known example of electrochemical corrosion, commonly known as rusting. This type of damage typically produces oxide(s) and/or salt(s) of the original metal. Corrosion can also refer to other materials than metals, such as ceramics or polymers, although in this context, the term degradation is more common.

• In other words, corrosion is the wearing away of metals due to a chemical reaction.• Many structural alloys corrode merely from exposure to moisture in the air, but the process can be strongly affected by exposure to certain substances . Corrosion can be concentrated locally to form a pit or crack, or it can extend across a wide area more or less uniformly corroding the surface. Because corrosion is a diffusion controlled process, it occurs on exposed surfaces. As a result, methods to reduce the activity of the exposed surface, such as passivation and chromate-conversion, can increase a material's corrosion resistance. However, some corrosion mechanisms are less visible and less predictable.

Rancidity• Rancidity is a very general term and in its most general meaning, it refers to the spoilage of a food in such a way that it becomes undesirable (and usually unsafe) for consumption. When people say that a food has "gone bad," what they're usually talking about is rancidity. Most of the time, but not always, rancidity can change the odours or flavours of a food in such a way that it becomes very unpleasant to smell or taste.

• While most any food can technically become rancid, this term applies particularly to oils. Oils can be especially susceptible to rancidity because their chemistry can make them exceptionally susceptible to oxygen damage. When food scientists talk about rancidity, they are often talking about a specific type of rancidity involving oxygen damage to foods, and this type of rancidity is called "oxidative rancidity." During the process of oxidative rancidity, oxygen molecules interact with the structure of the oil and damage its natural structure in a way that can change its odour, its taste, and its safety for consumption.

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