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8.5D: Recognize that chemical formulas are used to identify substances and determine the number of atoms of each element in chemical formulas containing subscripts.
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8.5D: Recognize that chemical formulas are used to identify substances and determine the number of atoms of each element in chemical formulas containing subscripts. 8.5F: Recognize whether a chemical equation containing coefficients is balanced or not and how that relates to the law of conservation of mass. Chemical Formulas and Equations
What does a chemical formula represent? • A chemical formula is a shorthand notation that uses chemical symbols and subscripts to represent the type and number of atoms present in a molecule. • What does the chemical formula C6H12O6 represent? A molecule that is made of 6 atoms of carbon, 12 atoms of hydrogen, and 6 atoms of oxygen.
What is a subscript? • Subscripts represent the number of atoms of the element present in one molecule of a substance. CH4 Subscript 4 represents 4 atoms of hydrogen. Carbon does not have a subscript so there is 1 atom of carbon.
What is a coefficient? • A coefficient is a number placed in front of a chemical symbol or formula that represents the number of molecules of the substance. 3CH4 3 molecules of the compound CH4 H H H C H H C H H H H C H H H
What does a chemical equation represent? • A chemical equation is a representation of the reactants and products in a chemical reaction using chemical symbols and formulas. 6H2O + 6CO2 C6H12O6 + 6O2 Yields Reactants Products The arrow separates the reactants and products and is read as “yields” or “to make.” What does this chemical reaction represent? 6 molecules of H2O reacts with 6 molecules of CO2 to make 1 molecule of C6H12O6 and 6 molecules of O2.
What is the Law of Conservation of Mass? • Matter cannot be created or destroyed, it can only change form. • The mass of all the reactants must equal the mass of all the products. • The type and number of atoms on the reactant side of the equation must be the same as the type and number of atoms on the product side of the equation.
How do you determine if a chemical equation is balanced? • A balanced chemical equation has the same type and number of atoms on the reactant and product side of the equation. 6H2O + 6CO2 C6H12O6 + 6O2 • 12 H atoms 12 H atom • 18 O atoms 18 O atoms • 6 C atoms 6 C atoms This chemical equation has the same type and number of atoms on each side of the equation so it is balanced.