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Matter: Interactions & Reactions

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Chris Gregory

on 25 October 2012

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Transcript of Matter: Interactions & Reactions

Chemical Reactions Matter: Interactions When atoms interact,
new substances are
formed. Striking a match

digesting your food

baking in the kitchen

using a battery

and many more! Examples of Chemical Reactions Clues that a Chemical Reaction
has taken place:
- Temperature change
(hotter or colder)
- Gas formation (bubbles)
- Color Change
- Precipitate (solid) formation
- Change in smell Chemical changes (reactions) are very
different from physical changes

- Chemical changes cannot be undone.

- Chemical changes are indicated by
the changes mentioned earlier.

- Physical changes can usually be undone
(at least to some extent) and do not result on any of the changes we mentioned earlier Let's Brainstorm.

With a partner, come up with and record 2 examples of chemical and physical changes (each) In a chemical reaction, bonds are broken,
and new bonds are formed.

The product is very different from
the original substances. Chemical Formulas

- A Chemical Formula is an easy way to write a compound’s name using chemical symbols and numbers to represent atoms.

Ex. HCl, NaCl A Chemical Formula shows how many of each kind of atom are present in a molecule of the compound Chemical formulas are like sheet music.
Any musician from any country can read
this piece of music.

The same is true of Chemical formulas and
Science students! A Chemical Equation uses chemical formulas, plus signs, and arrows to describe a Chemical Reaction The Reactants, carbon and oxygen, are the starting materials in this reaction.

The Products, in this case carbon dioxide, are the substances formed from a reaction Reactants

Reactants are the starting materials in a chemical reaction and are to the left of the yield sign (arrow) Product

- The product is the end result of a chemical reaction and is on the right side of the yield sign The Law of Conservation of Mass

-This law states that mass cannot be created or destroyed in chemical reactions.

-In other words, you will have the same type and number of atoms
in the reactants and products. Balancing Equations

- To ensure that a chemical reaction is "balanced", we must count the number of each type of atom on both sides of the yield sign. Important Information for Equations

- Coefficient - Big number before a compound.
You multiply every atom in the compound by this number. This number tells you how many MOLECULES there are. - Subscript

This is the little number to the right of a chemical symbol. This applies only to the chemical symbol in front of it.

If a subscript comes after parentheses, it applies to every symbol in the parentheses. Let's take a look. Let's Practice! PreAP:

Endothermic Reactions vs.
Exothermic Reactions

- In an endothermic reaction, energy is taken in, and the energy of the reactants is less than that of the products (ex. photosynthesis, vinegar and baking soda). This usually feels cold.
- In an exothermic reaction, energy is
given off. The energy of the product is more than that of the reactants (ex. lighting a match). This usually feels warm. Watch out! Sometimes this can be confusing--

Sometimes physical changes, like Carbon Dioxide bubbles in soda or food dye in water or something being heated (like soup), may make us think they are chemical changes.

Just remember that if YOU are heating or changing the color of something, that it is only a physical change! Compound

- Atoms of different elements chemically bonded together.
ex. HCl


- Two or more atoms bonded together. Can be two atoms of the same element.
ex. O2 Organic Compounds

Remember that most organic compounds contain one or more of:
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