210.1 Reactions and Equations Chemical Reaction- process by which the atoms of one or more substances are rearranged to form different substances
3a new substance is formed!! Chemical ReactionNa Cl = NaCl (Salt)a new substance is formed!!
4Evidence of a Chemical Reaction 1. Temperature changeExothermic - Release of energy in the form of heat or lightEndothermic – absorb heat (feels cold)
52. A Color change3. Odor4. Gas bubbles5. Formation of a solid(precipitate)
6Chemical EquationsReactant- starting substances in a reactionProduct- substances formed during the reactionNa Cl2 NaClReactants Products
7Reactants YIELD Products Reactants Products (left side) (right side) An arrow reads as yields and separates reactants from products and indicates direction of reaction --points to rightReactants YIELD ProductsReactants Products(left side) (right side)
8When there are two or more reactants or products a plus sign separates each reactant or product. reactant 1 + reactant product 1 + product 2and yields and(s) Solid (l) Liquid(g) Gas (aq) Aqueous – dissolved in water
9Word EquationsUses words to indicate the reactants and products of chemical reactions.Ex:Iron + chlorine → iron (III) chlorideRead: “iron and chlorine react to produce iron (III) chloride”
10Skeleton EquationsUses chemical formulas to identify reactants and productsEx:Fe (s) + Cl2 (g) → FeCl3 (s)Usually they are not balanced!!
11Chemical EquationsChemical Equation- uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction.
12C. Balancing a Chemical Equation The equation must show that the number of atoms of each reactant and each product are equal on BOTH sides of the arrow.
13To balance an equation you must find the correct coefficients for the chemical formulas in the skeleton equation.2Fe (s) + 3Cl2 (g) → 2FeCl3 (s)coefficients
14Coefficient- number written in front of a reactant or product 1. Is a whole number (not a fraction)2. Tells smallest number of particles of the substance involved in the reaction
15Steps for Balancing Equations 1.Write the skeleton equation for the reaction.
16A suggestion:Draw boxes around all the chemical formulas. This is the step that people frequently don't do. If it helps YOU… Ignore them.You're drawing those boxes so that you'll be sure not to mess around with the formulas to balance the equation.Here's what the equation looks like:
172. Count the atoms of the elements in the reactants (before). 3. Count the atoms of the elements in the products (after).Make an element inventory!!!!!
184. Write/Change the coefficients in front of each of the boxes until the inventory for each element is the same both before and after the reaction. Now, what happens when we put a number in front of a formula? Basically, anything in that box is multiplied by that number.5 H x 2 = 10 HydrogenKeep changing the coefficients until the number of atoms of each element is equal on both sides of the equation.H2
19We can see that on the left side of the inventory, there is one atom of sodium and on the right there are two. The solution: Stick a "2" in front of the sodium hydroxide on the left side of the equation so that the numbers of sodium atoms are the same on both sides of the equation.Then update your inventory!! But the others still don't match up. What to do?
20Using your amazing powers of mathematics (and hopefully not needing to use a calculator), you can see that two multiplied by the number two becomes four. That's what you need to do. How? Put a "2" in front of the water on the right side of the equation to make the hydrogens balance out. Now that this is done, you should make a new inventory that looks something like this:Since both sides of the inventory match, the equation is now balanced!
215. NEVER change a subscript!! You can’t change any subscripts because that would change the chemical composition of a molecule, which would change the entire reaction and create something different altogether.
226.Write the coefficients in front of the substances in the equation in their lowest possible ratio. 4H2O Fe 2Fe2O3 + 4H2All the coefficients are divisible by 2Should be:2H2O Fe Fe2O3 +2H27. Check your work!
2310.2 Classifying Chemical Reactions video- 5 chem rx animations.mp4
24Synthesis Reaction- a chemical reaction in which two or more substances react to produce a single productEx: 2Na (s) + Cl2 (g) → 2NaCl (s)Two or more reactants become one product
32element + cmpd element + cmpd Single-replacement Reaction- a reaction in which the atoms of one element replace the atoms of another element in a compoundEx: Cu (s) + 2AgNO3 (aq) → 2Ag (s) + Cu(NO3)2 (aq)element + cmpd element + cmpd