How do you know when a chemical reaction has occurred? Chemical Reactions How do you know when a chemical reaction has occurred?

REVIEW During a physical change, a substance changes its form but remains the same substance. A chemical change turns one or more substances into different substances that usually have different properties.

Chemical Reactions What is a chemical reaction?

A chemical reaction is a system of chemical changes that involves the breaking and reforming of chemical bonds to create new substances. Write definition of chemical reaction in notes

Products and reactants In chemical reactions, you start with reactants. They are combined to make the new substances called products. Write definition of reactants and products in otes

Reactants Products

In chemical reaction, NO new atoms are created or destroyed, just rearranged! Copy into notes

Conservation of Mass The mass of the reactants equals the mass of the products since the atoms are the same. Copy into notes

Alka-Seltzer and Water Do the demo H2O + Na(HCO3)    CO2  +  NaOH  +  H2O

Chemical Equations A chemical equation is a way to show the exact numbers of atoms and compounds in a chemical reaction. The arrow shows the direction the reaction goes, from reactants to products. Use the printed notes Reactants Products

Numbers in equations

2H2O Means H2O H= 4 O=2

Atoms in baking soda NaHCO3 Na= 1 H= 1 C= 1 O= 3 Sodium bicarbonate

Atoms in carbon dioxide CO2 C= 1 O= 2

Chemical reactions must be balanced

Balanced or not? The reaction combines hydrogen and oxygen molecules.

10.1 Chemical equations Count the atoms to see if there are the same number of each type of atom on the reactant and product sides of the equation. not balanced.

Yes, it follows conservation of mass because it’s balanced Balanced or not? O= 2 O=2 H= 4 H=4 Yes, it follows conservation of mass because it’s balanced

On the molecular level, dissolving of a solid (like sugar) occurs when molecules of solvent interact with and separate molecules of solute

In chemical reaction, NO new atoms are created or destroyed just rearranged! Copy into notes