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Chapter 2: Chemical Reactions Section 1: Observing Chemical Changes How can matter and changes in matter be described? PowerPoint Presentation
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Chapter 2: Chemical Reactions Section 1: Observing Chemical Changes How can matter and changes in matter be described? - PowerPoint PPT Presentation


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Chapter 2: Chemical Reactions Section 1: Observing Chemical Changes How can matter and changes in matter be described? In terms of two kinds of properties- physical properties and chemical properties Changes in matter can be described in terms of physical or chemical changes

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Chapter 2: Chemical ReactionsSection 1: Observing Chemical ChangesHow can matter and changes in matter be described?
  • In terms of two kinds of properties- physical properties and chemical properties
  • Changes in matter can be described in terms of physical or chemical changes
what is a physical property
What is a physical property?
  • A characteristic of a substance that can be observed without changing the substance into another substance
  • Examples: ice melting, color, hardness, texture, shine, etc.
what is a chemical property
What is a chemical property?
  • A characteristic of a substance that describes its ability to change into other substances
  • Examples: burning magnesium, rusting
what is the difference between a physical and a chemical reaction
What is the difference between a physical and a chemical reaction?
  • A change in matter that produces one or more new substances is a chemical change, or chemical reaction
  • Physical change examples: braiding your hair, squashing a marshmallow
  • Chemical change examples: burning of gasoline, burning a marshmallow
how can you tell when a chemical reaction occurs
How can you tell when a chemical reaction occurs?
  • Chemical changes occur when bonds break and new bonds form
  • Chemical reactions involve two main kinds of changes that you can observe-formation of new substances and changes in energy
what are some changes in properties that indicate a chemical change
What are some changes in properties that indicate a chemical change?
  • Precipitate – a solid that forms from a solution during a chemical reaction
  • Color change may indicate a chemical reaction
  • Gas production – bubbles
how do you categorize changes in energy
How do you categorize changes in energy?
  • Endothermic – A reaction in which energy is absorbed
    • Examples: baking soda and vinegar gets cooler when combined
  • Exothermic – A reaction that releases energy in the form of heat
    • Examples: burning of airplane fuel
section 2 describing chemical reactions what information does a chemical equation contain
Section 2: Describing chemical reactionsWhat information does a chemical equation contain?
  • Chemical equations use chemical formulas and other symbols instead of words to summarize a reaction
  • Reactants – substances you have at the beginning
  • Products – new substances produced when the reaction is complete
what does the principle of conservation of mass state
What does the principle of conservation of mass state?
  • That in a chemical reaction, the total mass of the reactants must equal the total mass of the products
  • Matter is neither created nor destroyed
what does open or closed system mean
What does open or closed system mean?
  • Open system – matter can enter from or escape to the surroundings
  • Closed system – matter is not allowed to enter or leave
what must a balanced chemical equation show
What must a balanced chemical equation show?
  • The same number of each type of atom on both sides of the equation
  • Represents the conservation of mass
  • Coefficients – a number placed in front of a chemical formula in an equation that tells you how many atoms or molecules of a reactant or product take place in the reaction
how do you balance chemical equations
How do you balance chemical equations?
  • Count the # of atoms of each element in the reactants & products
  • ID element that is not equal on both sides
  • Add coefficient to the front of the formula that will make the # = on both sides for that element
sample problems
Sample Problems

Sample Problem:

Zn + HBr  H2 + ZnBr2

Multiply HBr x 2 to correct (balance)

Zn + 2HBr  H2 + ZnBr2

try these
Try these!!

2

2

  • Na + Cl2 NaCl
  • Ca + Cl2  CaCl2
  • H2O  H2 + O2
  • N2 + H2  NH3
  • Al2O3  Al + O2
  • P4 + O2  P4O6
  • Fe + H2O  Fe3O4 + H2

2

2

3

2

4

3

2

3

3

4

4

what is a synthesis reaction
What is a synthesis reaction?
  • When two or more substances combine to make a more complex substance
    • A + B  AB
    • 2H2 + O22H2O
  • Example: hydrogen and oxygen to make water
what is a decomposition reaction
What is a Decomposition reaction?
  • Breaking down compounds into simpler products
    • AB  A + B
    • 2H2O2 2H2O + O2
  • Example: Hydrogen peroxide decomposes into water and oxygen gas
what is a replacement reaction
What is a replacement reaction?
  • When one element replaces another in a compound, or when two elements in different compounds trade places
  • Example: copper metal obtained by heating copper oxide with carbon
  • Single (one element replaces another)
    • AB + C  AC + B
    • Zn + 2HCl  ZnCl2 + H2

or double (elements appear to trade places with another compound)

    • AB + CD  AC + BD
    • NaCl + AgF  NaF +AgCl
section 3 controlling chemical reactions how is activation energy related to chemical reactions
Section 3: Controlling Chemical ReactionsHow is activation energy related to chemical reactions?
  • The minimum amount of energy needed to start a chemical reaction
  • All chemical reactions need a certain amount of activation energy to get started
what factors affect the rate of a chemical reaction
What factors affect the rate of a chemical reaction?
  • Surface area – the greater the surface area that faster the reaction (ex. Chewing)
  • Temperature – raising the temperature causes particles to move faster and therefore have more energy; they also come into contact more often; lowering temperature slows things down
  • Concentration – amount of substance in a given volume; increased concentration-increased reaction
  • Catalysts – increases the rate of a reaction by decreasing the energy needed to start
    • Enzymes: biological catalysts
  • Inhibitors – material used to decrease the rate of reaction (ex. preservatives in food)