Presentation on theme: "Chapter 10 Chemical Reactions. 10.1 Reactions and Equations Chemical Reaction- process by which the atoms of one or more substances are rearranged to."— Presentation transcript:
Chapter 10 Chemical Reactions
10.1 Reactions and Equations Chemical Reaction- process by which the atoms of one or more substances are rearranged to form different substances
Chemical Reaction Na + Cl 2 = NaCl (Salt) a new substance is formed!!
Evidence of a Chemical Reaction 1. Temperature change Exothermic - Release of energy in the form of heat or light Endothermic – absorb heat (feels cold)
2. A Color change 3. Odor 4. Gas bubbles 5. Formation of a solid (precipitate)
Chemical Equations Reactant- starting substances in a reaction Product- substances formed during the reaction Na + Cl 2 NaCl Reactants Products
An arrow reads as yields and separates reactants from products and indicates direction of reaction --points to right Reactants YIELD Products Reactants Products (left side) (right side)
When there are two or more reactants or products a plus sign separates each reactant or product. reactant 1 + reactant product 1 + product 2 andyields and (s) Solid(l) Liquid (g) Gas(aq) Aqueous – dissolved in water
Word Equations Uses words to indicate the reactants and products of chemical reactions. Ex: Iron + chlorine → iron (III) chloride Read: “iron and chlorine react to produce iron (III) chloride”
Skeleton Equations Uses chemical formulas to identify reactants and products Ex: Fe (s) + Cl 2 (g) → FeCl 3 (s) Usually they are not balanced!!
Chemical Equations Chemical Equation- uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction.
C. 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.
To balance an equation you must find the correct coefficients for the chemical formulas in the skeleton equation. 2Fe (s) + 3Cl 2 (g) → 2 FeCl 3 (s) coefficients
Coefficient- 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
Steps for Balancing Equations 1.Write the skeleton equation for the reaction.
A 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:
2. 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!!!!!
4. 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 2 5 x 2 = 10 Hydrogen Keep changing the coefficients until the number of atoms of each element is equal on both sides of the equation. H2H2
We 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?
Using 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!
5. 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.
6.Write the coefficients in front of the substances in the equation in their lowest possible ratio. 4H 2 O + 4Fe 2Fe 2 O 3 + 4H 2 All the coefficients are divisible by 2 Should be: 2H 2 O + 2Fe Fe 2 O 3 +2H 2 7. Check your work!
10.2 Classifying Chemical Reactions video- 5 chem rx animations.mp4
Synthesis Reaction- a chemical reaction in which two or more substances react to produce a single product Ex: 2Na (s) + Cl 2 (g) → 2NaCl (s) Two or more reactants become one product
Combustion Reaction- Oxygen combines with a substance and releases energy in the form of heat and light Ex : 2H 2 (g) + O 2 (g) → 2H 2 O The products are always Carbon dioxide CO 2 and Water H 2 O
Decomposition Reaction- a single compound breaks down into two or more elements or new compounds Ex: 2NaN 3 (s) → 2Na (s) + 3N 2 (g)
Mercury(II) oxide Mercury + Oxygen
Single-replacement Reaction- a reaction in which the atoms of one element replace the atoms of another element in a compound Ex: Cu (s) + 2AgNO 3 (aq) → 2Ag (s) + Cu(NO 3 ) 2 (aq) element + cmpd element + cmpd
2 Al + 3 CuCl 2 2 AlCl Cu
Double-replacement Reaction- positive and negative ions of two compounds switch places. Ex: KCN (aq) + HBr (aq) → KBr (aq) + HCN (g) cmpd cmpd cmpdcmpd
Precipitate – a solid produced during a chemical reaction in a solution All Double-replacement reactions produce: Precipitate Gas Water
10.3 Reactions in Aqueous Solutions
When a substance dissolves in water a solution forms. Solution – homogeneous mixture (looks the same throughout)
Solute – substances dissolved in water. Solvent – the most plentiful substance in the solution, usually water. Aqueous solution – a solution in which the solvent is water.