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evidence of chemical reactions, writing equations

2 main types of evidence of a chemical reaction...

change in properties and change in energy

changes in properties include...

precipitation, gas production, and color change

changes in energy include...

endothermic reactions & exothermic reactions


a solid that forms from 2 solutions mixing

One observable characteristic of a chemical reaction is

the production of new materials that have properties different than those of the starting materials

color change

like leaves changing color in the fall

gas production

like oxygen bubbles forming during photosynthesis

endothermic reaction

energy is absorbed, substance feels cooler

exothermic reaction

energy is released as heat, substance feels warmer

The second observable characteristic of a chemical reaction is

a change in energy

Chemical reactions occur when

chemical bonds break, or new bonds form

chemical equations are

a shorter, easier way to show chemical reactions using symbols instead of words

Formulas identify

the elements in the compound and the ratio of atoms that make up a substance

The subscript tells you

the number of atoms of an element in a molecule

If a letter symbol in a chemical formula doesn't have a subscript

the number 1 is understood

A chemical equation tells you

the substances you start with and the substances you get at the end


the materials you have at the beginning


the different materials you have when the reaction is complete

A chemical equation uses formulas & symbols to

show the reactants and products of a chemical reaction

conservation of mass says

the amount of matter involved in a chemical reaction does not change

during a chemical reaction

the total mass of the reactants must equal the total mass of the products

because of the conservation of mass,

during a chemical reaction, matter is not created or destroyed

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