CH 8 CHEMICAL REACTIONS AND EQUATIONS SECTIONS 1 AND 2

Chemical Change One or more substances changes into one or more new substances. Evidence: Changes in energy:

Chemical Change Evidence Formation of new substances 1. ________ (bubbles in solution, pressure change in a closed system) 2. _________(a cloudy solid that settles out of solution) 3. _________ change 4. _________change

Collision Theory of Reactions  Chemicals must come into contact (________)  The contact must be in the correct orientation (___________________)  There must be enough energy for the reactants to get started (________________)

Chemical equations Equations are used to describe chemical processes Equations show physical states of matter (s, l, g) and some reaction conditions.

In words: Solid magnesium and oxygen gas when heated, react to form solid Magnesium Oxide.

Symbols used in chemical equations Pt  ( ) Solid ( ) Liquid ( ) Gas ( ) aqueous  

2 arrows means reversible reaction  Reversible… reaction “goes both ways” The products form, and can “un-form”  Most reactions that happen in your cells are reversible reactions

Elemental forms  Most elements come naturally in ‘ones’ Ex. Sodium = Na Magnesium = Mg Iron = Fe Exceptions: 1. Diatomic Gases 2. Non Gases

Write unbalanced equations for the following:  Aqueous Sodium Hydroxide and hydrogen chloride gas  React to form  Water and aqueous Sodium Chloride  Unbalanced means don’t put any coefficients

Write out this reaction using symbols:  Solid Lithium reacts with water, forming lithium hydroxide solution and Hydrogen gas.

In a reaction  Mass is neither created nor destroyed. closed system Your bag was a closed system. No atoms were added or removed. They were rearranged. Law of Conservation of Mass

Rules for Balancing Equations 1. Count the number and type of each element on the reactants’ side. Do the same for the products’ side. 2. Check to see if there are any elements not in balance. 3. Use coefficients to balance any elements that are not equal. 4. Coefficients affect all parts of the molecule that follows.

__ N 2 + __ H 2  __ NH 3  Coefficients:  multiply through the whole molecule.  Must be a whole number  Are placed in front of molecules not between.

Write balanced equations for the following:  Sodium Hydroxide and hydrogen chloride React to form  Water and Sodium Chloride

Balance this reaction:  Lithium reacts with water  Forming lithium hydroxide and Hydrogen gas

Write the equation and balance it using coefficients  Lithium reacts with oxygen  To produce Lithium oxide  Silver Nitride is produced when silver metal reacts with nitrogen from the atmosphere.

Warm Up  How many Oxygen atoms are there in each of the following compounds? 1. NO 2 _______ 2. 2 NO 2 _____ 3. 2 Mg(NO 3 ) 2 _______

Balance the following  Li + H 2 O  LiOH + H 2  C 6 H 12 O 6 + O 2  H CO 2

Warm Ups  What is the mass of E 24 molecules of Oxygen gas?  How many formula units are there in 50.0g of Magnesium Chloride?  How many atoms are there in the same amount of MgCl 2 ?