CHANGES IN MATTER NOTES

I. Matter

A) Anything that has mass (weight) and volume (space).

B) Can be either pure substances or mixtures

1. Pure substances have properties the same throughout, such as in a

a) Compound - 2 or more elements chemically joined.

Example: water (H₂O) is

made of 2 elements, hydrogen(H) and oxygen(O);

sucrose(table sugar, C₁₂H₂₂O₁₁) is made of the 3 elements carbon(C), hydrogen, and oxygen.

b) Element - 1 type of atom alone is present.

Example: In gold, there are only gold atoms (Au) present; in diamond, only carbon (C) is present.

2. Mixtures contain 2 or more substances, but not chemically joined. The properties aren’t the same throughout. Types of mixtures are

a) mechanical mixture - you can see 2 or more different parts present.

Example: in cereal, you have the cereal particles, the milk, air bubbles, etc.

b) suspension - small solids are scattered in a liquid.

Example: orange or tomato juice has bits of solid in liquid juice which can be seen under magnification.

c) solutions - 2 substances are so completely mixed they look like one substance.

Example: salt or sugar water

II. Types of Changes

A) Physical Change

1. No new substance is produced.

2. The change can be reversed by reversing the conditions.

Example: melting ice is a physical change because water is still present, and the ice can be reformed by cooling the water.

B) Chemical Change

1. New substances with new properties are produced.

2. It is difficult or impossible to reverse the change by reversing the conditions.

3. Energy changes may be very noticeable with chemical change.

Example: a piece of wood or paper burning is a chemical change, because new substances (smoke, ash, gases) are made and they cannot easily reform the wood. 4. How can you tell a chemical change has occurred?

a) A new color appears.

b) Heat or light is given off.

c) Bubbles of gas form.

d) A precipitate (solid) forms in a liquid.

e) It is difficult to reverse.

III. Chemical Reactions

A) Reactants are the beginning substances.

B) Products are the new substances that form.

C) Word equations show the reactants and products in a chemical change.

1. separate the reactants with “+”  signs.

2. Follow reactants with an arrow that points to the products.

3. Use “+” signs between products.

Example: the elements hydrogen and oxygen react to form the compound water. The word equation is

hydrogen + oxygen --> water

Example: What are the reactants in the word equation

copper + oxygen --> copper  oxide

Answer: copper and oxygen

D) Common Reactions

1. Corrosion - rusting, or chemical eating away of a metal by oxygen and water.

a) paint can protect metals from corrosion;

b) attaching another, more reactive metal (like zinc or magnesium) can protect a metal from corrosion;

Example: attaching zinc to an iron ship keeps the iron from corroding.

c) aluminum protects itself by forming a protective coating of aluminum oxide.

2. Combustion (burning) - oxygen is a reactant, and products are water, carbon dioxide gas, and heat. Example: when gasoline burns (combusts), the reaction is

gas + oxygen --> water + carbon dioxide + heat        

 

IV. Mass and Chemical Change

A) Law of Conservation of Mass - “In a chemical reaction, the total mass of the reactants is always equal to the total mass of the products.” This means that total weight is constant in any chemical change.

Example: If the total mass of gas + oxygen = 10.0 grams, then the total mass of water + carbon dioxide produced in combustion = 10.0 grams too!