Name: ___________________________________________________ Date: 10/15/13 Period: ______ NOTES

Chemical Reactions Notes: The Law of Conservation of Mass

What happens in a Chemical Reaction?

  • Chemical ___________ in the reactants are _____________, then atoms are ____________ to form new substances (______________).
  • The amount of ____________ does not ____________ during a chemical reaction, the __________ are only rearranged to form _______ substances.  
  • This is evidenced (____________) in a balanced chemical _________________

What is a Chemical Equation?

  • A chemical equation is a way that scientists ________________ a chemical ____________ that has occurred. It shows the __________________ of atoms in a chemical reaction.
  • It contains the chemical ____________ of the substances involved in the reaction.  
  • An ___________ is used to distinguish between the reactants and ____________, and can be understood as meaning “__________” or “___________”.
  • _______________ are the substances broken apart or combined in a chemical reaction (what you ___________ with!) and they are located on the _______ side of the arrow in a chemical ______________.  
  • _______________ are new substances formed in a chemical reaction (what you _________ with!) and they are located on the ___________ side of the arrow in a chemical ________________.
  •  Ex:    C      +        O2           CO2 
  • This equation says “carbon __________ with oxygen to _____________ (make) carbon dioxide.”
  • The arrow shows the ________________ of the reaction:
  • _____________  _______________

What is the Law of Conservation of Mass?

  • When substances ___________ with each other, many ________________ can take place, but in every case the total amount of __________  afterward is the _________ as before.
  • Discovered by Lavoisier—_____________ chemist
  • Law of Conservation of _________:  in a chemical rxn, _________ (________) is neither ___________________ nor ___________________
  • Mass of                                = mass of products 
  • All ____________ present in the reactants are also present in the _____________. There must be the ___________________ of atoms in the products and reactants.

Mass Stays the SAME

  • The __________ of the products must be the __________ as the mass of the ___________
  • You do not magically gain or lose mass!!!
  • Example: If you have ____ grams of Na react with ____ gram of Cl to make NaCl, you know you must have ____ grams of NaCl in the products!
  • Na  +  Cl  NaCl

__ g   + __g  ___g

Number of Atoms Stays the SAME

  • You must have the _________ number of atoms of _______________________ on both sides of the equation.
  • If you have ____ atoms of oxygen in the reactants, you must have ____ atoms of oxygen in the products. (You do not magically gain or lose atoms!!!)
  • This is NOT something someone made up; it’s how chemical reactions happen in ____________!

How can I tell how many atoms of each element there are?

  • Coefficient: the “_________” number written in ___________ of a chemical ___________ that tells you how many _________________ of that substance there are.
  • Ex: 5 H2O = ____ molecules of water
  • Draw:
  • The _________________ tells you how many ___________ of each element there are.
  • The coefficient __________ the subscript tells you how many _________________ of that element are present.
  • 5 H2O = ____ atoms of Hydrogen, ____ atoms of Oxygen
  • If there is _____ coefficient, then there is only _______ molecule of that substance!

What does it mean to Balance a Chemical Equation?

  • Sometimes we have to “______________” a chemical equation to make sure that we have the ___________ number of ___________ of each element on ___________ sides of the equation. To do this, we change the number of _________________ by changing the ___________________ (NEVER THE _____________________!!!) until we have the same number of atoms of each ______________ on both sides. When we do this, we are saying how many _______________ of each substance must be ______________ before the reaction will _____________________ (remember: this is not something scientists made up; this is how the reactions happen in ____________!).

How do I know if a Chemical Equation is Balanced?

  • Check the number of _____________ of each element on both sides of the equation (reactants and products).
  • If the number of atoms of each element is the _________________ on both sides, then the equation is balanced.
  • Example:

H2      +      O2           H2O   : _______________________________

2H2      +      O2           2H2O   : _____________________________