Chemical Reactions

Law of Conservation of Mass

Matter can not be

created or

destroyed, although

it may be

rearranged.

Lavoisier, 1788

Chemical Reactions change that occurs when atoms

rearrange themselves

A process in which one or more substances are changed into others

Chemical Reaction

•How do you know if a chemical reaction has occurred?

Creation or loss

of heat

• Anytime two

chemicals are

combine resulting in a

temperature change,

that is evidence that

heat is being added or

lost from the products

and a chemical

reaction had occurred.

Evidence of Chemical Reactions

•Temperature Change

•Heat is absorbed by the substances causing the temperature to decrease

•Heat is released by the substances causing the temperature to increase

Production of a gas

(bubbles)

• When you mix chemical and see

bubbles or foaming, that is

evidence that a new gas has

formed

• This is a new substance which

means that a chemical reaction

must have occurred

• The only exception is when you boil

a liquid by adding heat

Evidence of Chemical Reactions

•Fizzing

•When a gas is formed it may try to escape causing bubbles

Evidence of Chemical Reactions

•Color Change

•This is evidence of a chemical reaction only when the other properties have also changed.

Chemical

Change

Not a

Chemical

Change

Evidence of Chemical Reactions

•Precipitate Formed

•Precipitate is a solid substance formed when liquids are combined

•Example – Sour Milk Clumps

Evidence of Chemical Reactions

•Light

•When a new substance is formed light energy can be produced.

Other Signs That a Chemical Reaction has occurred •Fire

•Rotting

•Breaking down (decomposition)

•Cooking

•Rusting (oxidation)

What chemical reactions have you experienced???

EXIT TICKET: 3-2-1 Chemical Reactions

• 3: Types of evidence that proves that a chemical change has occurred

• 2: Examples of chemical reactions

• 1: Way that chemical reactions are different than physical changes.