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Chemistry Unit: Chemical Reactions

Chemistry Unit: Chemical Reactions. Physical Properties. Physical property – characteristic that can be observed without changing the composition of a substance. Appearance includes things that can be observed with the senses States of matter – solid, liquid, or gas

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Chemistry Unit: Chemical Reactions

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  1. Chemistry Unit: Chemical Reactions

  2. PhysicalProperties • Physical property – characteristic that can be observed without changing the composition of a substance • Appearance includes things that can be observed with the senses • States of matter – solid, liquid, or gas • Volume, mass, and density • Melting point, boiling point, and others

  3. Chemicalproperties • Chemical property – characteristic that cannot be observed without altering the substance • Ability to burn • Tendency to rust • Reaction to other substances such as acids and bases

  4. Physical changes • Physical change – form or appearance of matter changes, but composition stays the same. • Change does not produce a new substance • Shape can change, but substance does not • Dissolving a solid into a liquid is a physical change

  5. Chemicalchanges • Chemical change: a change in the substance’s composition • During a chemical reaction: • Energy may be gained or released • Color can change • Substances may change odor • Formation of a gas or the precipitation of a solid

  6. Chemicalreaction • Chemical Reaction – one or more substances are changed into a new substance, with new physical and chemical properties. • Chemical Changes result in a new substance with a new chemical formula

  7. Signs of a chemical change • Heat is released or absorbed, measured by a temperature change • Unexpected color change • Release of a gas • odor, steam, or bubbles • Formation of a precipitate • when a solid forms from reacting liquids

  8. Chemicalequation • Chemical Equation – represents the chemical combining of elements and/or compounds (reactants and their products) • Reactants – substances that are about to react on the left of an equation. • Products - the new substance(s) that are produced on the right • Reactants yield Products

  9. Chemical equation continued • Coefficient – number that indicates how many compounds or elements are present in chemical reaction, written in front of the formula or symbol. • Subscript – smaller number written after a symbol that tells how many atoms are present in a compound

  10. Review chemical equation • CH4 + 2 O2 → CO2 + 2 H2O • What are the reactants? • What are the products? • What is the term for the small 4 by the CH4 and what does it mean? • How many oxygen atoms are reactants? • How many oxygen atoms are products? • CH42O2 • CO22H2O • Subscript, there are 4 Hydrogen atoms • 4 • 4

  11. Law of conservation of mass • The mass of the products of a chemical reaction must be the same as the mass of the reactants in that reaction. • The number and kind of atoms must be equal on both sides of the equation. • Atoms are never lost or created in a chemical reaction; however, they do change partners.

  12. Energyreactions Exothermic VS Endothermic

  13. ExothermicReactions • Therm refers to heat energy • Exo refers to out • Exothermic reaction • a reaction in which energy is released during the reaction. The products have less energy than the reactants. • Exothermic reactions feel warm • Energy is written on the product side of the equation.

  14. Endothermicreactions • Endo refers to in • Reaction in which energy is absorbed during the reaction. The products have more energy than the reactants. • Endothermic reactions feel cold • Energy is written on the reactant side of the equation.

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