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6th Grade Science 5-1, 5-2 Observing Chemical Reactions & Writing Chemical Equations
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
like leaves changing color in the fall
like oxygen bubbles forming during photosynthesis
energy is absorbed, substance feels cooler
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
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