Chemical Reactions | 01-21-2016

What are four pieces of evidence of a chemical change?

1. Bubbling (a new gas is forming) 2. Turns cloudy (a new solid is forming) 3. Temperature change (chemical bonds are changing) 4. Color change (a new substance is forming)

How do you balance a chemical equation?

1. Start with the correct chemical formula for each compound that appears as a reactant or product. 2. Write down the equation for the reaction (un-balanced.) 3. Count the # of atoms of each element in the reactants and the products. 4. Adjust the coefficient of each reactant or product until the total # of each type of atom is the same on both sides of the equation. *** You CANNOT change the subscript.

Define a "chemical reaction."

A process that rearranges chemical bonds to create new substances.

Define "endothermic."

A reaction is endothermic if it uses more energy than it releases. (cold)

Define "exothermic."

A reaction is exothermic if it releases more energy than it uses. (heat)

Define "decomposition." Give an example.

A single compound is broken down to produce two or more smaller compounds. i.e. 2H2O --> 2H2 + O2

Describe what happens during a "physical change."

A substance changes its form but remains the same substance. (i.e. liquid water freezes into solid ice)

Define a "chemical equation."

An equation of chemical formulas that shows the exact numbers of atoms and compounds in a chemical reaction. i.e. 2H2 + O2 --> 2H2O

Why are baking soda and vinegar such good ingredients for making a volcano model?

Baking soda and vinegar are reactants. Baking soda (solid) and vinegar (liquid) make a product (gas.) The sodium bicarbonate (NaHCO3) and the acetic acid (HC2H3O2) in the vinegar. There are four elements: C, O, Na, and H. The reaction must arrange these same atoms into the products. They become sodium acetate (NaC2H3O2), water (H20), and carbon dioxide (CO2.) No new atoms were created.

What is "activation energy?"

Energy needed to break chemical bonds in the reactants to start a reaction.

How do you know that chemical reactions conserve mass? (Conservation of Mass Law)

If there are the same number of atoms of an element in the product and reactant, the mass is conserved. The atoms just rearrange themselves into new compounds.

Define "single displacement." Give an example.

One element replaces a similar element in a compound. i.e. Fe + CuCl2 --> Cu + FeCl2

Describe what happens during a "chemical change."

One or more substances turn into different substances into different substances that usually have different properties. (i.e. burning wood into ashes)

Define "double displacement." Give an example.

Two elements replace similar elements in a compound. i.e. NaOH + HCl --> HOH + NaCl

Define "synthesis." Give an example.

Two or more substances chemically combine to form a new compound. i.e. 4Fe + 3O2 --> 2Fe2O3