Chemical Reactions Alter Arrangements of Atoms Physical Science Chapter 7 Section 1

Atoms Interact in Chemical Reactions A chemical reaction produces new substances by changing the way in which atoms are arranged A chemical reaction produces new substances by changing the way in which atoms are arranged Bonds are broken and new bonds form between different atoms Bonds are broken and new bonds form between different atoms After a chemical reaction, the new arrangements of atoms form different substances After a chemical reaction, the new arrangements of atoms form different substances

Physical Changes Substances may have some different properties after a physical change, but it is still the same substance Substances may have some different properties after a physical change, but it is still the same substance You know that water can exist in three different physical states: Solid (Ice), Liquid (Water), and a Gas (Water Vapor) You know that water can exist in three different physical states: Solid (Ice), Liquid (Water), and a Gas (Water Vapor) Substances can go through different kinds of Physical Changes Substances can go through different kinds of Physical Changes

Chemical Changes Water can also go through a chemical change Water can also go through a chemical change Water can be broken down into hydrogen and oxygen molecules by a chemical reaction called electrolysis Water can be broken down into hydrogen and oxygen molecules by a chemical reaction called electrolysis Hydrogen and oxygen are used as rocket fuel for the space shuttle, this process is the opposite of electrolysis Hydrogen and oxygen are used as rocket fuel for the space shuttle, this process is the opposite of electrolysis

Reactants and Products Reactants are the substances present at the beginning of a chemical reaction Reactants are the substances present at the beginning of a chemical reaction Products are the substances formed by the chemical reaction Products are the substances formed by the chemical reaction Reactants and products can be elements or compounds, depending on the reaction taking place Reactants and products can be elements or compounds, depending on the reaction taking place

Evidence of Chemical Reactions Color Change Color Change Formation of a Precipitate – Many chemical reactions form products that exist in a different physical state from the reactants. A solid product called a precipitate may form when chemicals in two liquids react. Formation of a Precipitate – Many chemical reactions form products that exist in a different physical state from the reactants. A solid product called a precipitate may form when chemicals in two liquids react. Formation of Gas Formation of Gas Temperature Change Temperature Change

Synthesis A new compound is formed by the combination of a simpler reactants. A new compound is formed by the combination of a simpler reactants.

Decomposition A reactant breaks down into simpler products, which could be elements or compounds A reactant breaks down into simpler products, which could be elements or compounds

Combustion One reactant is always oxygen and one product is almost always water One reactant is always oxygen and one product is almost always water

Rates of Chemical Reactants can vary Concentration – Concentration measures the number of particles present in a certain volume. A high concentration of reactants means that there is a large number of particles that can collide and react Concentration – Concentration measures the number of particles present in a certain volume. A high concentration of reactants means that there is a large number of particles that can collide and react Surface Area – Large pieces of a material could be broken into smaller pieces before the reaction starts. Doing this increases the surface area of the material. Surface Area – Large pieces of a material could be broken into smaller pieces before the reaction starts. Doing this increases the surface area of the material.

Rates of Chemical Reactants can vary Temperature – The rate of a reaction can be increases by making the particles move faster. Temperature – The rate of a reaction can be increases by making the particles move faster. The most common way to make the particles move faster is to add energy to the reactants, which will raise their temperature The most common way to make the particles move faster is to add energy to the reactants, which will raise their temperature Chemical reactions can also be slowed or stopped by decreasing the temperature of the reactants Chemical reactions can also be slowed or stopped by decreasing the temperature of the reactants

Catalysts A Catalyst is a substance that increases the rate of a chemical reaction but is not itself consumed in the reaction A Catalyst is a substance that increases the rate of a chemical reaction but is not itself consumed in the reaction In living things, catalyst called enzymes are absolutely necessary for life In living things, catalyst called enzymes are absolutely necessary for life