4TH GRADING EXAMS IN SCIENCE

• Physical change


  A substance is converted into one or more new substances that have different formulas and properties
• Physical change


  • Water boils to form water vapor
  • Sugar dissolves in water to form a solution
  • Copper is drawn into thin copper wires
  • Pepper is ground into flakes
• Chemical change


  • Iron, which is gray and shiny, combines with oxygen to form orange-red rust
  • Shiny, silver metal reacts in air to give a black, grainy coating
  • A piece of wood burns with a bright flame, and produces heat, ashes, carbon dioxide, and water vapor
• Chemical reaction


  A process in which a substance/s is/are changed into one or more new substances
• Chemical equation


  Uses chemical symbols to show what happens during a chemical reaction
• Chemical reaction


  • Build a model airplane
  • Prepare a new recipe
  • Mix a medication
• Reactants


  The starting material/s in a chemical reaction
• Products


  The substance/s formed as a result of a chemical reaction
• Types of chemical reactions


  • Combination reaction
  • Decomposition reaction
  • Single replacement
  • Double replacement
  • Combustion reaction
• Combination reaction


  Two or more elements or compounds bond to form one product
• Decomposition reaction


  A single compound breaks down into two or more simpler substances
• Replacement reaction


  One element in a compound is replaced by another element
• Double replacement


  Two compounds exchange ions to form two new compounds
• Combustion reaction


  A substance reacts with oxygen to produce heat, light, and new products
• Collision


  The reactants must collide
• Orientation


  The reactants must align properly to break and form bonds
• Energy


  The collision must provide the energy of activation
• Three Conditions Required for a Reaction to Occur

  • Collision
  • Orientation
  • Energy
• Activation energy


  The amount of energy required to break the bonds between atoms of the reactants
• Heat of reaction


  The difference between the energy of the reactants and the energy of the products
• In an exothermic reaction

  The energy of the products is lower than the energy of the reactants, heat is released
• Exothermic reactions


  • Reaction of aluminum and iron(III) oxide
  • The thermite reaction
• In endothermic reactions


  The energy of the products is higher than that of the reactants, heat is absorbed
• Endothermic reactions


  • Hydrogen and iodine react to form hydrogen iodide
• Rate of reaction


  The amount of reactant used up, or the amount of product formed, in a certain period of time
• Reactions with low activation energies


  Go faster than reactions with high activation energies
• Factors affecting rate of reaction


  • Temperature
  • Concentration of reactants
  • Addition of catalysts
  • Surface area
• As temperature increases


  Kinetic energy of reactants increases, more collisions with required activation energy
• For every 10 °C increase in temperature, most reaction rates approximately double
• When body temperature rises


  Increase in pulse rate, rate of breathing, and metabolic rate
• When reactants are added


  More collisions between reactants, reaction goes faster
• Increasing reactant concentration


  • Giving a patient with breathing difficulty a higher oxygen content breathing mixture
• Catalyst


  Lowers the energy of activation by providing an alternate pathway with a lower energy requirement
• In the body, biocatalysts called enzymes make most metabolic reactions go at the rates necessary for proper cellular activity
• Stoichiometry


  Concerned with finding the relative quantities of reactants and products in a chemical reaction
• Law of Conservation of Mass


  Matter is neither created nor destroyed in a chemical reaction. The total mass of the reactants is equal to the total mass of products.
• Antoine Lavoisier


  • Father of modern chemistry, discovered the role played by oxygen in combustion
• In chemical reactions, even though matter changes in form, its mass always stays the same
• Chemical formula


  Tells us the number and kinds of atoms a substance has, which we then use to determine the mass of the substance to use in an experiment
• Chemical reactions in the body


  • Converting food into molecules that build muscles and move them
  • Converting carbon dioxide and water into carbohydrates in leaves of trees and plants