Science PDF - Physical and Chemical Changes

1. Physical Changes Definition: A physical change alters the form or appearance of a substance but does not change its chemical composition. Key Characteristics: Reversible: The original substance can be recovered. No new substances are formed. Changes in physical properties (e.g., shape,...

1. Physical Changes Definition: A physical change alters the form or appearance of a substance but does not change its chemical composition. Key Characteristics: Reversible: The original substance can be recovered. No new substances are formed. Changes in physical properties (e.g., shape, size, state of matter). Examples: Melting: Solid to liquid (e.g., ice melting into water). Freezing: Liquid to solid (e.g., water freezing into ice). Evaporation: Liquid to gas (e.g., water evaporating into steam). Condensation: Gas to liquid (e.g., steam condensing into water droplets). Sublimation: Solid to gas (e.g., dry ice sublimating into carbon dioxide gas). Deposition: Gas to solid (e.g., frost forming on a cold surface). Cutting, bending, crushing: Changing the shape or size of a substance. Importance: Understanding physical changes is essential for various applications, such as separating mixtures and understanding the properties of matter. 2. Chemical Changes Definition: A chemical change involves the formation of new substances with different chemical compositions and properties. Key Characteristics: Irreversible: The original substance cannot be easily recovered. New substances are formed. Changes in chemical properties (e.g., flammability, reactivity). Evidence of Chemical Change: Color Change: A change in the color of a substance often indicates a chemical reaction. Gas Production: The formation of bubbles or gas indicates a chemical change. Heat or Light Production: The release or absorption of heat or light is a common indicator of a chemical change. Smell or Taste Change: A change in the smell or taste of a substance can indicate a chemical change. Examples: Burning: Combustion reaction (e.g., wood burning). Rusting: Oxidation of iron (e.g., iron reacting with oxygen and water). Cooking: Chemical changes occur when food is cooked. Baking: Chemical reactions occur when baking soda and baking powder are used. Digestion: Chemical breakdown of food in the body.  Importance: Chemical changes are fundamental to many natural processes and technological advancements, including the production of energy, the development of new materials, and the understanding of biological processes. Factors Affecting Chemical Change Temperature: Heat can increase the rate of chemical reactions. Concentration: Higher concentrations of reactants can lead to faster reactions. Presence of Catalysts: Catalysts speed up chemical reactions without being consumed in the process. Surface Area: Increasing the surface area of reactants can increase the rate of reaction. Physical Properties Definition: Physical properties can be observed or measured without changing the chemical composition of the substance. Key Characteristics: Can be observed without altering the substance's chemical makeup. Can be measured using various tools and techniques. Examples: color, texture, odor, density, melting point, boiling point, magnetism, conductivity. Mass and Weight Mass: Refers to the amount of matter in an object. Measured in grams (g). Weight: Refers to the force of gravity acting on an object. It depends on both mass and the gravitational field. Volume Definition: The amount of space an object occupies. Measurement: Measured in units like milliliters (ml) or cubic centimeters (cm³). Density Definition: A substance's mass per unit of volume. It describes how tightly packed the matter is. Formula: Density = Mass / Volume Importance: Density helps us understand how substances will behave in different situations (e.g., floating or sinking). Insulators and Conductors Insulator: A material that does not allow heat or electricity to flow easily through it. Examples: wood, rubber, oil. Conductor: A material that allows the flow of charge (electricity) or heat. Examples: gold, silver, steel, copper, seawater, diamond. Chemical Properties  Definition: Chemical properties describe how a substance reacts with other substances. They involve changes in the chemical composition of the substance. Key Characteristics: Can only be observed by changing the substance's chemical makeup. Examples: flammability, reactivity, acidity, toxicity. Flammability Definition: The ability of a substance to burn or ignite. Examples: Alcohol, methane gas, gasoline. Reactivity Definition: The ability of a substance to react with other substances. Example: Oxidation occurs when oxygen combines with a substance. Acidity Definition: A substance's ability to donate hydrogen ions (H+). Example: Acid rain. Toxicity Definition: The ability of a substance to harm humans or animals. Example: Mercury. Sedimentation Definition: Sedimentation is the process of separating a mixture by allowing heavier, insoluble particles to settle at the bottom of a container. How it Works: Heavier particles settle due to gravity. Lighter particles remain suspended in the liquid. The rate of sedimentation is influenced by factors like particle size, density, and the viscosity of the liquid. Examples: Sand and water: Sand settles to the bottom, leaving clear water above. Milk and cream: Cream rises to the top due to its lower density. Key Points: Density: Density plays a crucial role in sedimentation. Heavier particles settle faster. Particle Size: Larger particles settle faster than smaller particles. Viscosity: A thicker liquid (higher viscosity) will slow down the sedimentation process. Decantation  Definition: Decantation is the process of carefully pouring off a liquid from a mixture, leaving the solid residue behind. How it Works: The mixture is allowed to settle, allowing the solid to settle at the bottom. The liquid layer is carefully poured off, leaving the solid behind. Examples: Separating sand from water: After sedimentation, the water is carefully poured off, leaving the sand behind. Separating oil from water: Oil and water do not mix, so oil floats on top of water. The oil can be decanted off. Key Points: Immiscibility: Decantation is most effective for separating mixtures where the components are immiscible (do not mix) and have different densities. Carefulness: It is important to pour the liquid slowly and carefully to avoid disturbing the settled solid. Crystallization Definition: Crystallization is a process where a solid forms from a solution, melt, or gas, with atoms or molecules arranging into a highly structured, repeating pattern called a crystal. Process of Crystallization Dissolving: The substance to be crystallized is dissolved in a suitable solvent. Cooling: The solution is slowly cooled, decreasing the solubility of the substance. Nucleation: Tiny crystals (nuclei) form as the solution becomes supersaturated. Growth: The nuclei grow by attracting more dissolved molecules, forming larger crystals. Separation: The crystals are separated from the remaining solution (mother liquor) by filtration or other techniques. Factors Affecting Crystallization Temperature: Cooling a solution decreases the solubility of the substance, promoting crystallization. Concentration: A higher concentration of the substance in the solution leads to faster crystallization. Solvent Choice: The solvent used should have a suitable solubility for the substance at different temperatures. Rate of Cooling: Slow cooling allows for the formation of larger, more well-defined crystals. Impurities: Impurities can affect crystal size and shape. Products of Crystallization Common Examples:  Candies: Sugar crystals form during candy making. Urea: A common fertilizer produced by crystallization. Borax: A cleaning agent obtained through crystallization. Sugar: Refined sugar is produced through crystallization. Table Salt: Sodium chloride crystals are obtained by crystallizing salt water. Key Concepts Solubility: The maximum amount of a substance that can dissolve in a solvent at a given temperature. Supersaturation: A solution that contains more dissolved substance than it can normally hold at that temperature. Nucleation: The formation of tiny crystals (nuclei) that act as starting points for crystal growth. Filtration Definition: Filtration is a separation technique used to separate solid particles from a liquid or gaseous mixture. It involves passing the mixture through a porous barrier (filter) that allows the liquid or gas to pass through but traps the solid particles. How Filtration Works Particle Size: The filter's pore size determines which particles are retained and which pass through. Density: The density of the solid particles and the liquid or gas influence the separation process. Solubility: The solubility of the solid in the liquid or gas can affect the efficiency of filtration. Types of Filtration Gravity Filtration: The mixture is poured through a filter paper or a funnel, allowing gravity to pull the liquid through. Vacuum Filtration: A vacuum is applied to the receiving flask, speeding up the filtration process. Pressure Filtration: Pressure is applied to the mixture, forcing the liquid through the filter. Components of a Filtration System Filter: A porous barrier that traps the solid particles. Examples: filter paper, mesh, cloth, sand, charcoal. Funnel: A cone-shaped device used to direct the mixture onto the filter. Receiving Flask: A container to collect the filtered liquid or gas Heterogeneous and Homogeneous Definition: A mixture is a combination of two or more substances where each substance retains its individual properties. Key Characteristics:  Components can be separated by physical means. No new substances are formed. The composition of a mixture can vary. Types of Mixtures Heterogeneous Mixtures: Definition: A heterogeneous mixture is a mixture where the components are not evenly distributed and can be easily distinguished. Characteristics: Components are visible. Components can be separated by simple methods like decantation or filtration. Examples: Sand and water Oil and water Salad Cereal and milk Homogeneous Mixtures: Definition: A homogeneous mixture is a mixture where the components are evenly distributed and appear as a single substance. Characteristics: Components are not visible. Components are difficult to separate by simple methods. Examples: Saltwater Sugar dissolved in water Air Coffee Solutions Definition: A solution is a special type of homogeneous mixture where one substance (solute) is dissolved completely into another substance (solvent). Key Characteristics: Solute particles are evenly distributed throughout the solvent. The solution has a uniform composition. Examples:  Sugar dissolved in water (sugar is the solute, water is the solvent). Salt dissolved in water (salt is the solute, water is the solvent). Importance of Mixtures Everyday Life: Mixtures are essential in our daily lives, from the food we eat to the air we breathe. Scientific Applications: Mixtures are used in various scientific and industrial processes, such as chemical reactions, pharmaceutical production, and food processing. This knowledge is essential for various scientific disciplines and has significant implications for technology and everyday life. Pure Substances Definition: A pure substance is a single kind of matter that cannot be separated into other kinds of matter by any physical means. Characteristics: Always has a definite and constant composition. Has unique and consistent properties. Examples: gold, water, sugar Elements Definition: An element is a pure substance that cannot be broken down into simpler substances by chemical reactions. Characteristics: Found on the periodic table. Each element has a unique atomic number. Examples: oxygen, carbon, iron Types of Elements Metals: Lustrous (shiny) appearance. Good conductors of heat and electricity. Malleable (can be hammered into sheets). Ductile (can be drawn into wires). Examples: gold, silver, copper Non-metals: Dull appearance. Poor conductors of heat and electricity. Brittle (easily broken).  Examples: oxygen, sulfur, carbon Metalloids: Have properties of both metals and non-metals. Semiconductors (conduct electricity under certain conditions). Examples: silicon, germanium Compounds Definition: A compound is a substance made up of two or more different elements that are chemically bonded together in fixed proportions. Characteristics: Can be broken down into simpler substances by chemical reactions. Has properties different from its constituent elements. Examples: water (H₂O), salt (NaCl), carbon dioxide (CO₂) Mixtures Definition: A mixture is a combination of two or more substances where each substance retains its individual properties. Characteristics: Components can be separated by physical means. No new substances are formed. The composition of a mixture can vary. Examples: Sand and water Salt and pepper Air Physical Properties: Characteristics of a substance that can be observed or measured without changing the substance's chemical composition (e.g., color, density, melting point). Chemical Properties: Characteristics of a substance that describe how it reacts with other substances (e.g., flammability, reactivity). Chemical Bond: A force that holds atoms together in a compound. Colloids Definition: Colloids and suspensions are types of mixtures where one substance (the dispersed phase) is spread throughout another substance (the dispersion medium). Key Difference: The main difference lies in the size of the dispersed particles. Colloids have particles smaller than those in suspensions, but larger than those in solutions. Suspensions  Definition: A suspension is a heterogeneous mixture where solid particles are dispersed in a liquid or gas. Characteristics: Particles are visible to the naked eye. Particles settle out over time. Can be separated by filtration. Not transparent. Examples: Muddy water Sand in water Dust in air Colloids Definition: A colloid is a homogeneous mixture where particles are dispersed throughout a medium, but are not dissolved. Characteristics: Particles are too small to be seen with the naked eye, but large enough to scatter light. Particles do not settle out over time. Cannot be separated by filtration. Can appear translucent or opaque. Examples: Milk Fog Paint Jello Types of Colloids Based on the Dispersed Phase and Dispersion Medium: Sol: Solid dispersed in a liquid (e.g., paint, milk of magnesia) Gel: Liquid dispersed in a solid (e.g., jelly, jam, cheese) Emulsion: Liquid dispersed in a liquid (e.g., milk, mayonnaise) Foam: Gas dispersed in a liquid (e.g., whipped cream, soap lather) Aerosol: Solid or liquid dispersed in a gas (e.g., smoke, fog) Importance of Colloids and Suspensions Everyday Applications: Colloids and suspensions are found in many everyday products and natural phenomena. Industrial Applications: Colloids are used in various industries, including food processing, cosmetics, and pharmaceuticals.