Changes of matter
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Changes of Matter. Physical Change- a change that alters the appearance or form of a substance but doesn’t produce a new substance. Ex: melting a sample of gold Chemical Change/Reaction- a change in matter that produces one or more new substances.

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Changes of Matter

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Changes of matter

Changes of Matter

Physical Change- a change that alters the appearance or form of a substance but doesn’t produce a new substance.

Ex: melting a sample of gold

Chemical Change/Reaction- a change in matter that produces one or more new substances.

Ex: Gas produced from vinegar and baking soda.


Evidence for chemical reactions

Evidence for Chemical Reactions

  • Gas Production

  • Change in Temperature/Energy

  • Change in Color

  • Change in Properties

  • Formation of a Precipitate


Changes in energy

Changes in Energy

  • Endothermic Reactions- a reaction in which energy is absorbed. Not all endothermic reactions result in a decrease in temperature.

    Ex:frying an egg

  • Exothermic Reactions- a reaction in which energy is released.

    Ex: the burning of airplane fuel


Chemical formulas

Chemical Formulas

  • A chemical formula is a combination of symbols that represents the elements present in the formula and the ratio of elements present.

    Ex: MgCl2 - One atom of magnesium for every two atoms of chlorine.

    Ratio is 1:2

    How many total atoms are present in the following:

    Pb(NO3)4H2SO42HNO3


What are chemical equations

What Are Chemical Equations?

  • Using formulas and symbols instead of words to represent a chemical reaction.

    Ex: CaCO3 ------- CaO + CO2

    Structure of an Equation

    *Reactants-substances you start with

    *Products-substances you end up with

    *Arrow means “yields”


Subscripts vs coefficients

Subscripts vs. Coefficients

  • Subscripts – A number that indicates the ratio of elements in a compound.

  • Ex: H2O Ratio 2:1

  • Coefficients – a number in front of a chemical formula in an equation that indicates how many molecules or atoms of each reactant and product are involved in a reaction.

  • Ex: 3H2O Three molecules of water


Conservation of mass

Conservation of Mass

  • During a chemical reaction, matter is not created or destroyed.

  • Total mass of the reactants equals the total mass of the products.

  • Open System – matter can enter from or escape to the surroundings. Ex: burning wood in a fireplace

  • Closed System – matter is not allowed to enter or leave.

    Ex: a chemical reaction in a sealed bag


Balancing equations

Balancing Equations

  • To describe a reaction accurately, a chemical equation must show the same number of each type of atom on both sides of the equation.

    Ex: 2H2O + O2 2H2O2

  • (4 hydrogen atoms and 4 oxygen atoms are present on both sides of the equation)


Try these

Try these!!

  • _Na + Cl2 _NaCl

  • Ca + Cl2  CaCl2

  • _H2O  _H2 + O2

  • N2 + _H2  _NH3

  • _Al2O3  _Al + _O2

  • P4 + _O2  P4O6

  • _Fe + _H2O  Fe3O4 + _H2


Changes of matter

Controlling Chemical ReactionsAll reactions require a certain amount of activation energy to get them started.

Activation energy – the minimum amount of of

energy needed to start a chemical reaction.


Factors that influence the rate of reactions

Factors that Influence the Rate of Reactions

  • Surface Area

  • Temperature

  • Concentration – amount of substance in a given volume

  • Use a Catalyst – a material that increases the rate of a reaction

  • Use an Inhibitor – a material that decreases the rate of a reaction


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