![]() Methane (CH4) is a molecule in which 4 hydrogen atoms are bonded to one carbon atom. New substances are formed the starting substances are called the reactants the new substances are called the products The mass of the reactants is always the same as the mass of the products after the chemical reaction. Endothermic reactions need to absorb heat from their surroundings to proceed.ġ9 Conservation of Mass Mass is conserved during chemical changes. When you strike a match you are providing the activation energy needed to cause a reaction between the chemicals in the match head and oxygen in the air.ġ8 All chemical reactions include a change in energy.Įxothermic reactions release energy to their surroundings usually in the form of heat. Vinegar (acetic acid): C2H4O2 Baking soda (sodium bicarbonate): NaHCO3 C2H4O2 + NaHCO3 -> C2H3O2Na + H2CO3 The products are sodium acetate and carbonic acid Carbonic acid quickly decomposes into carbon dioxide and water: H2CO3 -> H2O + CO2 The CO2 is what you see foaming and bubbling in this reaction.ġ6 Burning Sugar Add heat Add more heat C12 H22O11 = Carbon + Water (H2O)Ĭarbon + Water (H2O) = Carbon + Water Vapor (H2O) Carbon + Hydrogen gas + Oxygen gasġ7 Activation Energy is the energy needed to start a chemical reaction.Įxample: A match won't light spontaneously. For example, when hydrogen reacts with oxygen the product is water vapor.Īcid-base reaction. atoms rearrange themselves during a chemical reaction to form different molecules and compounds. Copy the following chart into your notes: Examples Properties before Properties after Evidence of a chemical change Bike Hair Alka Seltzer and water Fireworksġ4 In a chemical change one or more substances combine or break apart to form new substances. Examples of Chemical Properties: pH: a measure of how acidic something is Flammability: a substances ability to burn Reactivity: The rate at which a substance reactsĨ Clues that indicate a chemical change has taken place include:Ĭolor change temperature change bubbling and fizzing note: boiling water is NOT a chemical change heat, light, or smoke is given off a solid (precipitate) is formed the change is difficult or impossible to reverseĩ Copy the following chart into your notes:Ĭompare and contrast the chemical properties of the new substance with the original after a chemical change. Water evaporates butter melts a can is crushed glass is broken modeling clay is shaped ripping paper boiling water sawing wood breaking a stick dissolving salt in waterĭescribe the object or substance can be observed or measured without changing the identity of the substanceĤ Review: Examples of Physical PropertiesĬolor odor size shape state (solid, liquid, gas, plasma) texture (smooth, rough, soft, bumpy) density (measured in g/ml and g/cm³) melting point/boiling point/freezing pointĪre determined by the arrangement of atoms in the molecules making up the object describe a object or substance based on its ability to change into a new substance with different properties cannot be observed with your senses must be tested aren’t as easy to observe as physical propertiesĦ Key Idea #7 Chemical changes occur when elements and/or compounds react or decompose to produce new substances.ħ Chemical Properties If the chemical properties of an object or substance have changed, then a chemical reaction has occurred. ![]() of the material can change the material itself is the same before and after the change The change can be “undone” Chemical change: The substances present at the beginning of the change are not present at the end new substances are formed.
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