Class 10 Chemistry Ch 1

Cheatsheet Content

### Chemical Reactions - **Definition:** Processes that involve rearranging atoms to form new substances with different properties. - **Indicators of a Chemical Reaction:** - Change in state (e.g., solid to gas) - Change in color (e.g., rust formation) - Evolution of a gas (e.g., bubbles) - Change in temperature (exothermic/endothermic) - Formation of a precipitate (solid settling from solution) #### Types of Reactions - **Reactants:** Substances that undergo chemical change. - **Products:** New substances formed after the reaction. **1. Combination Reaction:** - Two or more reactants combine to form a single product. - **General form:** $A + B \rightarrow AB$ - **Example:** $2H_2(g) + O_2(g) \rightarrow 2H_2O(l)$ (Formation of water) - **Example:** $CaO(s) + H_2O(l) \rightarrow Ca(OH)_2(aq)$ (Slaking of lime) **2. Decomposition Reaction:** - A single reactant breaks down into two or more simpler products. - Often requires energy (heat, light, electricity). - **General form:** $AB \rightarrow A + B$ - **Types of Decomposition:** - **Thermal Decomposition:** By heating. - **Example:** $CaCO_3(s) \xrightarrow{\text{Heat}} CaO(s) + CO_2(g)$ (Limestone decomposition) - **Electrolytic Decomposition (Electrolysis):** By electricity. - **Example:** $2H_2O(l) \xrightarrow{\text{Electricity}} 2H_2(g) + O_2(g)$ (Water electrolysis) - **Photolytic Decomposition (Photolysis):** By light. - **Example:** $2AgCl(s) \xrightarrow{\text{Sunlight}} 2Ag(s) + Cl_2(g)$ (Used in black and white photography) **3. Displacement Reaction:** - A more reactive element displaces a less reactive element from its compound. - **General form:** $A + BC \rightarrow AC + B$ - **Example:** $Fe(s) + CuSO_4(aq) \rightarrow FeSO_4(aq) + Cu(s)$ (Iron displacing copper) - **Reactivity Series:** (Most to least reactive, approximate for metals) K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Ag > Au **4. Double Displacement Reaction:** - Exchange of ions between two reactant compounds. - **General form:** $AB + CD \rightarrow AD + CB$ - Often results in the formation of a precipitate, gas, or water. - **Example (Precipitation):** $Na_2SO_4(aq) + BaCl_2(aq) \rightarrow BaSO_4(s) + 2NaCl(aq)$ (Formation of white precipitate BaSO$_4$) - **Example (Neutralisation):** $HCl(aq) + NaOH(aq) \rightarrow NaCl(aq) + H_2O(l)$ (Acid-base reaction) **5. Oxidation and Reduction (Redox Reactions):** - **Oxidation:** - Addition of oxygen - Removal of hydrogen - Loss of electrons (OIL - Oxidation Is Loss) - **Reduction:** - Removal of oxygen - Addition of hydrogen - Gain of electrons (RIG - Reduction Is Gain) - **Redox Reaction:** Reactions where oxidation and reduction occur simultaneously. - **Oxidizing Agent:** Substance that oxidizes another substance and itself gets reduced. - **Reducing Agent:** Substance that reduces another substance and itself gets oxidized. - **Example:** $CuO(s) + H_2(g) \xrightarrow{\text{Heat}} Cu(s) + H_2O(l)$ - $CuO \rightarrow Cu$: Reduction (loss of oxygen) - $H_2 \rightarrow H_2O$: Oxidation (gain of oxygen) - CuO is the oxidizing agent, $H_2$ is the reducing agent. #### Effects of Oxidation in Everyday Life - **Corrosion:** Gradual eating away of metals by the action of air, moisture, or a chemical on their surface (e.g., rusting of iron, tarnishing of silver, green coating on copper). - **Rancidity:** Oxidation of fats and oils in food items exposed to air, leading to unpleasant smell and taste. - **Prevention:** Adding antioxidants, packaging in nitrogen gas, refrigeration, storing in airtight containers. ### Chemical Equations - **Definition:** A symbolic representation of a chemical reaction using chemical formulas. - **Reactants** are written on the left, **products** on the right, separated by an arrow ($\rightarrow$). - **Coefficients:** Numbers placed in front of formulas to balance the equation. - **State Symbols:** Indicate the physical state of reactants and products: - $(s)$ - solid - $(l)$ - liquid - $(g)$ - gas - $(aq)$ - aqueous (solution in water) #### Balancing Chemical Equations - Law of Conservation of Mass: Mass cannot be created or destroyed in a chemical reaction. Therefore, the number of atoms of each element must be equal on both sides (reactants and products). - **Hit and Trial Method:** 1. Write the unbalanced equation. 2. Start balancing with the compound containing the maximum number of atoms. 3. Balance atoms one by one (metals, non-metals, oxygen, hydrogen, usually in that order). 4. Check if the number of atoms of all elements are balanced on both sides. - **Example 1 (Unbalanced):** $Fe(s) + H_2O(g) \rightarrow Fe_3O_4(s) + H_2(g)$ - **Example 1 (Balanced):** $3Fe(s) + 4H_2O(g) \rightarrow Fe_3O_4(s) + 4H_2(g)$ - **Example 2 (Unbalanced):** $CH_4(g) + O_2(g) \rightarrow CO_2(g) + H_2O(l)$ - **Example 2 (Balanced):** $CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(l)$ #### Information Conveyed by a Chemical Equation - Reactants and products involved. - Physical states of substances. - Relative number of moles of reactants and products. - Conditions for the reaction (e.g., heat, catalyst, pressure) indicated above/below the arrow. - **Example:** $CO(g) + 2H_2(g) \xrightarrow{340 \text{ atm}} CH_3OH(l)$ (Methanol synthesis)