Chemical Changes and Reactions
How do you tell when a chemical reaction occurs?
2 main types of changes that you can observe- 1:formation of new substances 2:changes in energy
Can you measure all the reactants and products in an open system like a fireplace? Why?
No, you can measure wood ashes, but not oxygen and other gases
When do chemical changes occur?
When bonds break and new ones form
What is a chemical change?
a change in matter that produces one or more new substances
What is one way that you can tell that a change in energy has occurred?
a change in temperature (endothermic- sometimes cooler exothermic- warmer)
What is a chemical property?
a characteristic of a substance that describes its ability to change into other substances
What is a chemical equation?
a short, easy way to show a chemical reaction, using symbols instead of words
What's an open system?
a system in which matter can enter from or escape to the surroundings
What's a closed system?
a system in which no matter is allowed to enter or exit
Examples of chemical properties?
a) burning b) tarnishing c) rusting
What kinds of changes should you look for that might indicate a chemical change has occurred?
a) color change b) a solid (precipitate) appears when 2 solutions are mixed c) a gas can be produced from solids or liquids
Examples of physical changes?
a) squashing b) bending c) crushing d) breaking e) cutting f) braiding
How are chemical equations written?
a) the formulas for the reactants are written on the left b) followed by an arrow (yields) c) formulas for the products are written on the right d) When there are 2 or more reactants or products, a plus (+) sign is used to separate them Reactant + Reactant --> Product + Product
Examples of a chemical reaction?
a) toasting a marshmallow- sugar changes into caramel b) the burning of gasoline in a car's engine (becomes exhaust)
Examples of physical properties?
a. color b. hardness c.texture d. shine e. flexibility f. ability to dissolve in water g. how well it conducts heat and electricity h. melting (and boiling) point
What is a physical change?
any change that alters the form or appearance of a substance, but that doesn't make the substance into another substance
What is matter?
anything that has mass and takes up space
What do chemical equations use instead of words to summarize a reaction?
chemical formulas and other symbols
Is the ability of water to rust a physical or chemical property?
chemical property
Another name for a chemical change?
chemical reaction
A change in energy always occurs in a chemical reaction. What two ways can energy change?
energy can either be absorbed (endothermic) or released (exothermic)
Example of a closed system?
food that is in a sealed container in the fridge that has begun to decay
In what terms can changes in matter be described?
physical changes and chemical changes
In what two terms can matter be described?
physical properties and chemical properties
Is the freezing point of water a physical or chemical property?
physical property
Products?
the new substances you have after the reaction is complete
What is the Law of Conservation of Mass?
the principle stating that matter isn't created or destroyed during a chemical reaction
What is chemistry?
the study of matter and how it changes
What are reactants?
the substances that you have at the beginning of the reaction
If you add vinegar to baking soda in ziploc bag, what should the mass of the products be equal to? Why might the result be more than expected in this reaction?
the sum of the masses of the bag, baking soda, and vinegar Some of the gas produced in the reaction may have escaped from the bag before it was closed
What must the total mass of the reactants always be equal to?
the total mass of the products
What do chemical formulas tell u?
what elements and how many of each make up the compound
What's an example of an open system?
wood fire burning in a fireplace in a home with a chimney
