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Chemical Reactions

Chemical Reactions. Chemical formulas and Equations Rates of Chemical Reactions. Chemical Formulas and Equations. Physical Change Changes that only affect its physical properties like size, shape, or whether it is a solid, liquid or gas There is no change of material

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Chemical Reactions

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  1. Chemical Reactions Chemical formulas and Equations Rates of Chemical Reactions

  2. Chemical Formulas and Equations • Physical Change • Changes that only affect its physical properties like size, shape, or whether it is a solid, liquid or gas • There is no change of material • You still have the same substance that you began with • Ie: crumple paper, cut up wood, changes of water from ice, to liquid to a gas

  3. Chemical Formulas and Equations • Chemical Change • A change that produces a new substance with properties different from those of the original substances • Things that show that a chemical reaction has occurred • Precipitate forms (when 2 liquids combine the new substance will drop out of solution..is not soluble) • Odor given off • Change of color • Temperature change

  4. Chemical Formulas and Equations • Chemical reaction occurs when a chemical change takes place • Anytime you have a new substance formed • Burning paper is a result of a chemical reaction • Folding paper is a result of a physical change because you still have paper, only change of shape

  5. Chemical Equations • Using chemical symbols of elements and chemical formula you can write a shorthand of a chemical reaction • The substances you begin with in a chemical reaction is called the reactants • The new substances that are formed is called the product • In a chemical reaction you can write the reactants and resulting products in a chemical equation using arrows (and is read as produces)

  6. Chemical Equations • Baking soda + vinegar gas + white solid • 2NaHCO3 + H4C2O2 2NaH3C2O2 + H2O + CO2 • Sodium hydroxide plus Sulfuric acid produces sodium sulfate and water 2NaOH + H2SO4 Na2SO4 + H2O

  7. Conservation of Mass • Antoine Lavoisier: mass of the product must be the same as the mass of the reactants • Chemical equations must show that there is the same kind and number of atoms that you began with as was formed • Every atom that appears on the reactant side of the equation is found on the product side

  8. Balancing Equations • Chemical equations must show the conservation of mass by having same kind and same numbers of atoms on both side of a chemical reaction • Ag + H2S Ag2S + H2 • (Silver tarnishes in presence of sulfur) • Notice that the number of atoms aren’t the same on both side • Need to count the atoms… you can’t change the formula but you can add a coefficient in front of the formula to balance equations

  9. Balancing Equations • Ag + H2S Ag2S + H2 • Notice there is 2 Ag’s on product side and only one on reactant side…. Add a coefficient of 2 in front of reactant silver • 2Ag + H2S Ag2S + H2 • 2 Ag’s, 2 H’s and 1 S • It is balanced

  10. Balancing Equations • Al + O2 Al2O3 • Aluminum and oxygen produces aluminum oxide • Not balanced (can only change the coefficient) • 4Al + 3O2 2Al2SO3

  11. Balancing Equations http://education.jlab.org/elementbalancing/index.html

  12. Energy in Chemical Reactions • Energy released • Heat, light, sound or other energy is given off • When bonds break in a chemical reaction new bonds form in the products and energy is given off • Energy found on product side of chemical reaction • Called an exothermic reaction • 2H2 + O2 2H2O + energy

  13. Energy in Chemical Reactions • Energy is Absorbed • Energy is required to form new products • Can absorb light, sound, heat • Called an endothermic reaction • Energy is placed on the reactant side of equations • 2H2O + energy 2H2 + O2 • Ice packs are example of endothermic reactions

  14. Rates of Chemical reaction • Activation Energy: starting a reaction • To start a chemical reaction a minimum amount of energy is required to begin the process • That energy required is its activation energy • For gasoline to burn energy needs to be introduced to begin the chemical reaction…. That energy (match) will begin the chemical process

  15. Reaction Rate • Rate refers to a change over time • Reaction rate refers to the speed at which chemical reactions takes place over time • Reactions rates in some industries is important because the faster the rate, the less the cost • Some faster reaction rates can hurt industries • Ripening fruit gives less time from field to markets • The slower the ripening rate increases the time it can be on shelves

  16. Reaction Rate • Temperature changes rate • Lowering the temperature slows down reaction rates • Meat in freezers, bacteria grows faster in higher temperatures, lower movement of molecules, less chance of causing chemical changes • Temperature affects Rate • Most chemical reactions speed up with increase in temperature because of faster moving molecules • Lowering temperature usually slows down reaction rate

  17. Reaction Rate • Concentration Affects Rate • Closer the reactant atoms and molecules to each other, the greater the chance of collisions between them and faster the reaction rate • Amount of substance present in a certain volume is called the concentration of that substance • Increasing the concentrations increases the number of particles of a substance per unit of volume

  18. Reaction Rate • Surface Area Affects Rate • If you increase the surface area you will increase its chance of reacting with other substances • Twigs broken up compared to logs to begin a fire • Crushing up materials into smaller pieces increases surface area

  19. Slowing down Reactions • Inhibitors slow down chemical reactions • Makes the process of chemical change longer • BHT on cereal packages slow down the spoilage of cereal and increase its shelf life

  20. Speeding up Reactions • Catalysts are substances that speed up a chemical reaction without entering into the chemical reactions • It produces the same amount of product faster • Catalytic Converters utilize metals (platinum) to produce CO2 and water , which is less harmful in cars fuel combustion. • Enzymes are catalysts that are large protein molecules that speed up reactions needed in cells to work properly • They help speed up conversion of food to fuel, build bone and muscle tissue, and converting energy by fitting structures together properly so that reactions can occur faster

  21. Speeding up Reactions • Proteases is a special type of enzyme that helps break down large protein molecules • Meat tenderizers • Contact lenses cleaning solutions breaks down protein from your eyes that collect on your lenses and cloud your view

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