Chemical reactions are phenomenon which we usually get to see around us in daily life also. Here we will get to read about them in detail. All chemical reactions occurs at atomic level, the outcome of which can be visible or measurable.
Important notes for Class 10 C.B.S.E. Board for 2023-24 Exam
Syllabus: Chemical reactions, Chemical equation, and Balanced chemical equation, implications of a balanced chemical equation, types of chemical reactions: combination, decomposition, displacement, double displacement, precipitation, endothermic exothermic reactions, oxidation and reduction.
Chemical Reaction:
Definition: A chemical reaction is a process in which one or more substances (reactants) are transformed into new substances (products) with different chemical and physical properties.
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| Chemical reactions definitions and many more |
Few important points:
- During a chemical reaction, bonds between atoms are broken and new bonds are formed, resulting in the creation of entirely different molecules.
- The total mass of the reactants is always equal to the total mass of the products, as dictated by the law of conservation of mass.
Here are a few examples of common chemical reactions:
Combustion Reaction:
- Example: Burning of methane (natural gas).
- Chemical Reaction: \(CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(l)\)
Single Replacement (Displacement) Reaction:
- Example: Reaction between zinc and hydrochloric acid.
- Chemical Reaction: \(Zn(s) + 2HCl(aq) \rightarrow ZnCl_2(aq) + H_2(g)\)
Acid-Base Neutralization Reaction:
- Example: Reaction between hydrochloric acid and sodium hydroxide.
- Chemical Reaction: \(HCl(aq) + NaOH(aq) \rightarrow NaCl(aq) + H_2O(l)\)
Photosynthesis:
- Example: Conversion of carbon dioxide and water into glucose in plants.
- Chemical Reaction: \(6CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_2\)
Fermentation:
- Example: Conversion of sugars into alcohol by yeast.
- Chemical Reaction: \(C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2\)
These examples showcase different types of chemical reactions and their diverse applications in various natural and industrial processes.
Chemical Equation:
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| Chemical Equations with Definitions and Examples |
Definition: A chemical equation is a symbolic representation of a chemical reaction.
Few important points:
- It uses chemical formulas and symbols to depict the reactants and products involved in the reaction.
- The equation provides a concise and structured way to communicate the details of the reaction, including the types and amounts of substances involved.
- The reactants are written on the left side of the arrow (\(\rightarrow\)), and the products are written on the right side.
Example of a simple chemical equation:
\[ 2H_2(g) + O_2(g) \rightarrow 2H_2O(l) \]
In this equation:
- \(2H_2\) and \(O_2\) are the reactants.
- \(2H_2O\) is the product.
- The coefficients (2 in front of \(H_2\) and \(H_2O\)) represent the ratio of moles in the reaction.
The equation states that two molecules of hydrogen (\(H_2\)) react with one molecule of oxygen (\(O_2\)) to produce two molecules of water (\(H_2O\)).
Now Let's cover the Chemical Reactions and Equations chapter in chemistry, including the characteristics of chemical reactions and some examples, along with simple chemistry laboratory experiments.
Understanding Balanced and Unbalanced Chemical Equations
Chemical equations are symbolic representations of reactions, showcasing the transformation of reactants into products. These equations, whether balanced or unbalanced, illustrate the conservation of mass and atoms in a reaction.
Balanced Chemical Equations:
A balanced chemical equation is one in which the number of atoms for each element in the reactants is equal to the number of atoms for that element in the products. This balance ensures the law of conservation of mass is upheld.
Unbalanced Chemical Equations:
An unbalanced chemical equation lacks an equal number of atoms of each element on both sides of the equation. This imbalance violates the law of conservation of mass and doesn’t accurately represent the reaction.
Steps to Write Balanced Chemical Equations:
1. Write the Chemical Equation:
Begin by writing down the chemical formulas of the reactants and products involved in the reaction.
2. Count Atoms on Each Side:
Count the number of atoms for each element on both sides of the equation. Start with elements that appear only once on each side.
3. Use Coefficients:
Introduce coefficients (whole numbers) before the chemical formulas to balance the equation. Adjust these coefficients to ensure the same number of atoms for each element on both sides.
Examples of Balanced and Unbalanced Equations:
Balanced Equations:
1. Combustion of Methane:
\[ CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(l) \]
- Steps to Balance:
- Count carbon and hydrogen atoms on both sides.
- Introduce coefficients to balance the atoms: 1:2:1:2 for CH₄:O₂:CO₂:H₂O.
2. Formation of Water:
\[ 2H_2(g) + O_2(g) \rightarrow 2H_2O(l) \]
- Steps to Balance:
- Count hydrogen and oxygen atoms on both sides.
- Adjust coefficients to balance the atoms: 2:1:2 for H₂:O₂:H₂O.
3. Neutralization of Hydrochloric Acid and Sodium Hydroxide:
\[ HCl(aq) + NaOH(aq) \rightarrow NaCl(aq) + H_2O(l) \]
- Steps to Balance:
- Count atoms of hydrogen, chlorine, sodium, and oxygen on both sides.
- The equation is already balanced; each element has the same number of atoms on both sides.
Unbalanced Equations:
1. Incomplete Combustion of Ethanol:
\[ C_2H_5OH(l) + O_2(g) \rightarrow CO_2(g) + H_2O(l) \]
- Unbalanced: The equation lacks balance in the number of oxygen atoms.
- Balanced: \( C_2H_5OH(l) + 3O_2(g) \rightarrow 2CO_2(g) + 3H_2O(l) \)
2. Decomposition of Hydrogen Peroxide:
\[ H_2O_2(aq) \rightarrow H_2O(l) + O_2(g) \]
- Unbalanced: Unequal oxygen atoms on both sides.
- Balanced: \( 2H_2O_2(aq) \rightarrow 2H_2O(l) + O_2(g) \)
3. Formation of Ammonia from Nitrogen and Hydrogen:
\[ N_2(g) + H_2(g) \rightarrow NH_3(g) \]
- Unbalanced: Unequal nitrogen atoms on both sides.
- Balanced: \( N_2(g) + 3H_2(g) \rightarrow 2NH_3(g) \)
Balancing chemical equations is crucial in accurately representing reactions according to the laws of conservation of mass and atoms. By following systematic steps and adjusting coefficients, one can ensure a balanced equation, reflecting the precise relationship between reactants and products in a chemical reaction.
Chemical Reactions
Chemical reactions are processes where substances undergo changes to form new substances. These reactions are represented by chemical equations, which show the reactants turning into products.
Characteristics of Chemical Reactions:
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| Characteristics of Chemical Equations |
1. Formation of New Substances:
- Chemical reactions result in the creation of new substances with different properties than the original ones.
Example: When a magnesium (Mg) ribbon is burnt in air or in the presence of oxygen, it gets converted into Magnesium Oxide. The process involves the burning of ribbon with sparkling white flame, and the ribbon gets converted into ashes.
Chemical Equation Involved:
\[ 2Mg + O_2 \rightarrow 2MgO \]
2. Change in Temperature:
- Reactions involve the absorption or release of energy. Endothermic reactions absorb energy, while exothermic reactions release energy.
Some chemical reactions are characterized by change in temperature, like while chemical reaction takes place. There can be either absorption of heat or releasing of heat.
2.1 Endothermic reaction
The reaction between barium hydroxide (\(Ba(OH)_2\)) and ammonium chloride (\(NH_4Cl\)) is an endothermic property and the formation of precipitates and is also a double displacement reaction.
The balanced chemical equation for this reaction is:
\[ Ba(OH)_2 + 2NH_4Cl \rightarrow 2NH_4OH + BaCl_2 + 2H_2O \]
When performing this reaction in a laboratory setup, you might notice a decrease in temperature in the surrounding area of the reaction mixture. The vessel might feel cooler to the touch or a thermometer placed nearby could register a drop in temperature.
2.1 Exothermic reaction
When quick lime reacts with water, then slaked lime is formed and a lot of heat energy is produced. The heat raises the temperature due to which the reaction mixture becomes hot.
The reaction between quicklime (calcium oxide, CaO) and water (\(H_2O\)) is highly exothermic and results in the formation of slaked lime (calcium hydroxide, \(Ca(OH)_2\)). This reaction is known as slaking of lime and is utilized in various applications, including construction, agriculture, and chemical processes.
The balanced chemical equation for this reaction is:
\[ CaO + H_2O \rightarrow Ca(OH)_2 \]
When performing this reaction in a laboratory setup, you might notice a increase in temperature in the surrounding area of the reaction mixture. The vessel might feel warmer to the touch or a thermometer placed nearby could register a rise in temperature.
3. Change in Color:
- Some reactions cause a change in color as new substances are formed.
Some chemical reactions are characterised by change in
colour. Few examples are as follows:
Table
1.3
Two examples of chemical equations showing
change in colour
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2. |
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When
Potassium Permanganate (KMnO4) reacts with Citric Acid (C6H8O7),
the purple colour of Potassium Permanganate disappears. i.e., the
reaction between Citric acid and Potassium Permanganate is characterised by
change in colour from purple to colourless. |
The
orange colour of acidified Potassium Dichromate (K2Cr2O7)
solution changes to green when Sulphur Dioxide (SO2) gas is
passed through it. i.e., the reaction between sulphur dioxide gas and
acidified potassium dichromate is characterised by change in colour from
orange to green. |
4. Evolution of Gas:
- Gas may be produced during a reaction, leading to the formation of bubbles or effervescence.
There are some chemical reactions which involves the
evolution of gases. Few examples are as follows:
Table
1.5 Two examples of chemical
reactions showing evolution of gas
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2. |
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When
zinc (Zn) reacts with dilute sulphuric acid (dil. H2SO4),
evolution of hydrogen gas takes place. The same experiment can also be done
by reacting zinc with the dilute hydrochloric acid. |
When
magnesium (Mg) reacts with dilute sulphuric acid (dil. H2SO4)
or dilute hydrochloric acid, the also the evolution of hydrogen gas takes
place. |
5. Change in State:
- The physical state of reactants and products may change (solid to liquid, liquid to gas, etc.).
Change in state means changing of form either from
solid to liquid, liquid to gas, gas to liquid like this. Some chemical
reactions involve change in physical states also. Few examples are as follows:
Table
1.4 Two examples of chemical
equations showing change in state
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1. |
2. |
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Melting of ice
in to water in one such example which involves the change of solid ice into
the liquid water. |
Burning of wax
candle leads to formation of liquid and carbon dioxide. |
6. Formation of precipitation:
- The physical state of reactants and products may change (solid to liquid, liquid to gas, etc.).
Precipitate is a solid insoluble compound which is
formed when chemical reaction takes place. Few examples are as follows:
Table
1.6 Two examples of chemical
reactions showing formation of precipitate
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1. |
2. |
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When
potassium iodide (KI) solution reacts with solution of lead nitrate
(Pb(NO3)2), a yellow precipitate of lead iodide is
formed. Thus, reaction between potassium iodide and lead nitrate is
characterised by formation of yellow precipitate of lead iodide. |
The
reaction between dilute sulphuric acid (dil. H2SO4)
and barium chloride (BaCl2) lead to the formation of white
precipitate of barium sulphate. This formation of white precipitate of barium
sulphate shows the reaction between sulphuric acid and barium chloride. |
Three examples of Chemical Reactions:
These are just three basic examples of types of chemical reactions, they are almost eight in total which you can access in detail in the types of chemical reactions section.
1. Combustion Reaction:
- Example: Burning of methane:
\[ CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(l) \]
2. Acid-Base Neutralization:
- Example: Reaction between hydrochloric acid and sodium hydroxide:
\[ HCl(aq) + NaOH(aq) \rightarrow NaCl(aq) + H_2O(l) \]
3. Precipitation Reaction:
- Example: Formation of a precipitate when silver nitrate reacts with sodium chloride:
\[ AgNO_3(aq) + NaCl(aq) \rightarrow AgCl(s) + NaNO_3(aq) \]
Chemistry Laboratory Experiments:
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| Chemistry Laboratory Experiments |
1. Identification of Gases:
- Experiment: Collecting and testing gases produced in reactions.
- Example: Testing for carbon dioxide by passing it through limewater.
2. Types of Reactions:
- Experiment: Performing various reactions to classify them.
- Example: Mixing solutions to observe precipitation, gas evolution, etc.
3. Electrolysis:
- Experiment: Passing electric current through a solution to observe decomposition.
- Example: Electrolysis of water to produce hydrogen and oxygen.
4. Rate of Reactions:
- Experiment: Measuring the speed of reactions under different conditions.
- Example: Investigating how temperature affects the rate of a chemical reaction.
5. Titration:
- Experiment: Determining the concentration of a solution using a titrant.
- Example: Titration of an acid with a base to find the concentration of the acid.
Remember, safety precautions should always be followed in laboratory experiments, and the experiments should be conducted under the supervision of an experienced instructor.
Day to day life examples of chemical reactions
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Day to day life examples of chemical reactions |
Chemical reactions are an integral part of our daily lives, and many natural and human-made processes involve chemical changes. Here are a few day-to-day life examples of chemical reactions:
1. Burning of Fuel:
- Example: Combustion of gasoline in a car engine.
- Chemical Reaction: \(2C_8H_{18} + 25O_2 \rightarrow 16CO_2 + 18H_2O\)
2. Cooking:
- Example: Baking a cake.
- Chemical Reaction: The reaction between baking soda and vinegar produces carbon dioxide, causing the cake to rise.
3. Respiration:
- Example: Breathing.
- Chemical Reaction: The breakdown of glucose in cells during cellular respiration.
\[ C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy} \]
4. Rusting of Iron:
- Example: Rust formation on a metal surface.
- Chemical Reaction: \(4Fe + 3O_2 \rightarrow 2Fe_2O_3\)
5. Digestion:
- Example: Breaking down food in the stomach.
- Chemical Reaction: Various hydrolysis reactions involving enzymes.
6. Photosynthesis:
-Example: Plants converting sunlight into energy.
- Chemical Reaction: \(6CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_2\)
7. Tarnishing of Silver:
- Example: Silverware becoming dull over time.
- Chemical Reaction: \(4Ag + O_2 + 2H_2S \rightarrow 2Ag_2S + 2H_2O\)
8. Fermentation:
- Example: Production of bread and yogurt.
- Chemical Reaction: The conversion of sugars into alcohol or acids by microorganisms.
9. Cleaning with Bleach:
- Example: Using bleach to disinfect surfaces.
- Chemical Reaction: \(2NaClO + 2HCl \rightarrow 2NaCl + 2H_2O + Cl_2\)
10. Battery Operation:
- Example: Using a battery to power a device.
- Chemical Reaction: In a common alkaline battery, zinc reacts with manganese dioxide and potassium hydroxide to produce electrical energy.
These examples illustrate the diverse ways in which chemical reactions play a role in our everyday experiences, from the food we eat to the processes that power various devices.
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