Chemical Changes and Reactions

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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


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