Chemical ChangeChemical Change
Observing, Describing, Controlling
Observing, Describing, Controlling
Observing Chemical ChangeObserving Chemical Change
• Matter can be described in two ways:– Chemical properties– Physical properties
• Matter can be described in two ways:– Chemical properties– Physical properties
Observing Chemical ChangeObserving Chemical Change
• Chemical Properties: The characteristics of a substance that describes it’s ability to change into a different substance. – EXAMPLE: In our magnesium lab, we
lit the magnesium on fire, watched it burn as it reacted with the oxygen in the air. This was its chemical property: flammability.
• Chemical Properties: The characteristics of a substance that describes it’s ability to change into a different substance. – EXAMPLE: In our magnesium lab, we
lit the magnesium on fire, watched it burn as it reacted with the oxygen in the air. This was its chemical property: flammability.
Observing Chemical ChangeObserving Chemical Change
• Physical Properties: a characteristic of a substance that can be observed without changing the substance into something new. – EXAMPLE: Frozen water (ice) melts at
0 degrees Celsius. The tops of the tables in this room are black and 4.5ft long.
• Physical Properties: a characteristic of a substance that can be observed without changing the substance into something new. – EXAMPLE: Frozen water (ice) melts at
0 degrees Celsius. The tops of the tables in this room are black and 4.5ft long.
Observing Chemical ChangeObserving Chemical Change
• Like the properties of matter, the changes it undergoes can be:– Physical Changes
OR– Chemical Changes
• Like the properties of matter, the changes it undergoes can be:– Physical Changes
OR– Chemical Changes
Observing Chemical ChangeObserving Chemical Change
• Physical Changes: Any change that alters the form, shape, or appearance of a substance but does not change it into a new substance. – EXAMPLE: If I were to toss fresh
berries into a blender and make a fruit smoothie- it would still be fruit, just mashed into smaller pieces.
• Physical Changes: Any change that alters the form, shape, or appearance of a substance but does not change it into a new substance. – EXAMPLE: If I were to toss fresh
berries into a blender and make a fruit smoothie- it would still be fruit, just mashed into smaller pieces.
Observing Chemical ChangeObserving Chemical Change
• Chemical Changes: a change that a substance undergoes where a totally new substance is the result. – EXAMPLE: In the magnesium lab, we
burned magnesium and after it’s chemical change the result was magnesium oxide. It was no longer metal!!
• Chemical Changes: a change that a substance undergoes where a totally new substance is the result. – EXAMPLE: In the magnesium lab, we
burned magnesium and after it’s chemical change the result was magnesium oxide. It was no longer metal!!
Observing Chemical ChangeObserving Chemical Change
• During a chemical change you have:– Reactants: the substance that is
being changed.– Products: the new substance formed
as a result of the chemical reaction.
• During a chemical change you have:– Reactants: the substance that is
being changed.– Products: the new substance formed
as a result of the chemical reaction.
Observing Chemical ChangeObserving Chemical Change
• REMEMBER: in order for a chemical reaction to have occurred- bonds must be broken and new bonds must be made!!!
• REMEMBER: in order for a chemical reaction to have occurred- bonds must be broken and new bonds must be made!!!
Observing Chemical ChangeObserving Chemical Change
• EVIDENCE that a CHEMICAL REACTION has occurred: – Change in properties– Change in energy
• EVIDENCE that a CHEMICAL REACTION has occurred: – Change in properties– Change in energy
Observing Chemical ChangeObserving Chemical Change
• Change in properties: color change, a solid forms (precipitate), formation of gas, and texture change.
• CAUTION!! Sometimes physical changes make it SEEM like a chemical change has occurred. Really THINK about the changes.
• Change in properties: color change, a solid forms (precipitate), formation of gas, and texture change.
• CAUTION!! Sometimes physical changes make it SEEM like a chemical change has occurred. Really THINK about the changes.
Observing Chemical ChangeObserving Chemical Change
• Change in Energy: During chemical changes, energy is either absorbed or released. – Endothermic reactions (heat enters)– Exothermic reactions (heat exits)
• (remember those words…??)
• Change in Energy: During chemical changes, energy is either absorbed or released. – Endothermic reactions (heat enters)– Exothermic reactions (heat exits)
• (remember those words…??)
Describing Chemical ChangesDescribing Chemical Changes
• Chemical equations are used to show/explain a chemical reaction. – This shows the reactants and
products of a reaction– They show the substances you start
with, on the left and the new substances on the right separated by an arrow.
• Chemical equations are used to show/explain a chemical reaction. – This shows the reactants and
products of a reaction– They show the substances you start
with, on the left and the new substances on the right separated by an arrow.
Describing Chemical ChangesDescribing Chemical Changes
• Generic formula looks like:
Reactant + Reactant ---> Product + Product
• Generic formula looks like:
Reactant + Reactant ---> Product + Product
Conservation of Mass (matter)Conservation of Mass (matter)• During Chemical reactions, atoms
cannot be created OR destroyed. • The total mass of the reactants
must equal the total mass of the products.
• During Chemical reactions, atoms cannot be created OR destroyed.
• The total mass of the reactants must equal the total mass of the products.
Conservation of Mass (matter) Conservation of Mass (matter) • In a chemical reaction, the number
of atoms stays the same- they are just rearranged. Therefore, the number of atoms in the reactants are the same as the number of atoms in the products.
• In a chemical reaction, the number of atoms stays the same- they are just rearranged. Therefore, the number of atoms in the reactants are the same as the number of atoms in the products.
Open and Closed SystemOpen and Closed System
• Sometimes it’s hard to understand where the matter comes from in a reaction.
• Matter can either come from an…– Open System
or a…– Closed System
• Sometimes it’s hard to understand where the matter comes from in a reaction.
• Matter can either come from an…– Open System
or a…– Closed System
Open and Closed SystemOpen and Closed System
• Open System: Matter can enter from or exit into the surroundings during a reaction.
• Closed System: Matter cannot enter or leave during the reaction.
• Open System: Matter can enter from or exit into the surroundings during a reaction.
• Closed System: Matter cannot enter or leave during the reaction.