Chemical Reactions

What is a chemical reaction? A process in which atoms are chemically combined or rearranged to make new substances.

What are the two parts of a chemical reaction? Reactants and products

What is a reactant? It is what you START with in a chemical reaction.

What is a product? It is your FINAL result in a chemical reaction.

How do you know a chemical reaction has occurred? Change of color Gas, light or sound is emitted Change in temperature A precipitate forms

What is an exothermic reaction? A reaction that feels warm/hot to you.

Why does it feel warm? Energy is released from the bonds breaking to form new compounds.

What is an endothermic reaction? One that feels cold to you.

Why does it feel cold? When the bonds break, they require more energy, so that energy is being absorbed from its surroundings.

How do you write chemical reactions? Reactants  Products

What does the  mean? Makes, yields, produces, etc

What are some symbols you will see in chemical reactions? + separates formulas (s) Solid (l) Liquid (g) Gas (aq) solid dissolved in water (aqueous) Catalyst compound Catalyst was used ^^^^^ electricity Δ Heat

Example Reactant (l) + Reactant (g)  product (s) + product (aq)

What is a catalyst? A coumpound that helps a reactions occur. It is not used in the reaction, which is why it is written on the arrow.

Do I look at it when I balance my reaction? NO!

What do you do once you have a chemical reaction? Balance the skeleton reaction.

Why do you have to balance an equation? You have to have equal numbers of each atom on either side of the equation.

Why do you have to have equal numbers? Law of Conservation of Matter- Nothing is ever created or destroyed

How do you balance equations? Use coefficients in front of the compounds

What are some hints to balancing? Make an inventory Save O and H for last If you have the same polyatomic ion on each side, keep it together in the inventory Sometimes water can split into H(OH) Reduce if necessary If elements are split, save for last.

Examples V 2 O 5 + CaS  CaO + V 2 S 5

NaNO 3 + PbO  Pb(NO 3 ) 2 + Na 2 O

H 2 SO 4 + Al(OH) 3  Al 2 (SO 4 ) 3 + H 2 O

What if I have a word equation to start? Write the formulas, then balance as always.

What is something to remember? BrINClHOF! If it just says Hydrogen, you actually write it H 2 All other single elements, stay single (mercury =Hg)

Calcium reacts with oxygen to produce calcium oxide

iron + oxygen  iron (III) oxide

Solid calcium carbonate reacts with aqueous hydrochloric acid to yield solid calcium chloride, carbon dioxide gas and liquid water.

How many different types of reactions are there? 5

What are they? Synthesis Decomposition Single Replacement Double Replacement Combustion

What is synthesis? When you make one new single compound from 2 or more A + B  AB

+  Sally Joey

Example Hydrogen and oxygen combine to make water.

What is decomposition? When one substance breaks apart into more substances. AB  A + B

 + Betty Billy

Example Hydrogen Peroxide (H 2 O 2 ) decomposes into Water and Oxygen gas.

What is single replacement? When a single element replaces one part of a formula, creating another single element. A + BC  B + AC

+ + Sally

Example Mg + CuSO 4  MgSO 4 + Cu

What is double replacement? When the ions of 2 different formulas trade places AB + CD  AD + CB

Example NaBr + MgS  Na 2 S + MgBr 2

What is combustion? You will have a compound and oxygen as reactants. CO 2 and H 2 O are always your products.

Example _________ + O 2  H 2 O + CO 2

How do you predict reaction products? It depends on the type of reaction.

How do you predict Synthesis Reactions? You need to take your two independent elements, look up the charges, and then swap and drop.

How do you predict Single Replacement Reactions? Cations always replace cations Anions always replace anions. Figure out what is single (cation or anion) and replace accordingly. Swap n Drop

How do you predict Double Replacement Reactions? Cations replace cations Anions replace anions Pair accordingly Swap n drop

How do you predict Combustion Reactions? Combustion Products are always CO 2 and H 2 O

Examples: CaCO 3 + HCl 

(Fe is iron (III)) Fe + CuSO 4 

H 2 + N 2 

MgCl 2 + Ca 3 (PO 4 ) 2 

Chromium (III) chloride reacts with Silver (I) nitrate

Combustion! C 4 H 10 + O 2 

Chlorine reacts with sodium bromide

Aluminum reacts with sulfuric acid

Mercury (II) reacts with phosphorus

Ammonium Iodide reacts with nitrogen gas

Lead (II) phosphate reacts with potassium chlorate

What types of products can you make? A gas (g) A precipitate (s) An aqueous substance (aq) A liquid (l)

What is a precipitate? An insoluble, solid product that is the result of a chemical reaction

What is an aqueous substance? A soluble compound that is dissolved into water.

How do you predict the precipitate in a product? Use a chart!

What does an exception mean on the chart? It means it goes to the other side if it is an exception.

What happens to H 2 CO 3 as a product? It automatically breaks apart into water and carbon dioxide.

What about other compounds if they are not on the chart? Water is always a liquid Carbon dioxide is always a gas.

What about the diatomic elements? All diatomic elements are gases EXCEPT – Bromine is a liquid – Iodine is a solid

What about all the other elements? All other elements are solids except – Mercury is a liquid