Unit 4: Chemical Reactions
Decomposition is basically the opposite of combination reactions. In decomposition.............
1 reactant breaks apart into 2 or more products.
Choose the correct set of coefficients to balance the following equation. Pb3O4 → Pb + O2
1,3,2
Choose the correct set of coefficients to balance the following equation. C2H4 + O2 → H2O + CO2
1,3,2,2
A combination reaction occurs when.........
2 or more reactants combine to form 1 product. This type of reaction is also called an addition reaction because the two reactants are added together.
Choose the correct set of coefficients to balance the following equation. Mg + O2 → MgO
2,1,2
Choose the correct set of coefficients to balance the following equation. P + O2 → P4O10
4,5,1
Which of the following conditions will increase the rate of a chemical reaction?
Adding a catalyst
When temperature rises:
As temperature increases the reactant molecules will move faster and have more kinetic energy. When the reactants collide they are more likely to exceed the activation energy required to break apart the bonds of the reactants so products can form. This means that more of the collisions will result in the formation of product thus increasing the rate of the reaction.
Physical Change
Changes that occur that do not involve changing of one substance into a new substance. May change the size, shape or state of the substance but not the chemical formula of the substance.
What condition does NOT have to be met for a chemical reaction to occur?
Collide and Bounce Back
Identify the type of reaction: C3H8 + 5O2 → 3CO2 + 4H2O
Combustion
Endothermic reactions draw the required energy from the surroundings. EX:
EX: If you are holding a test tube containing ammonium nitrate and you add water, you will feel the test tube getting colder. The process of the ammonium nitrate dissolving in the water is endothermic so it draws heat from the surroundings which include the water, the test tube and your hand making them feel colder.
Activation Energy
Energy needed to get a reaction started The concept of activation energy is similar to climbing a hill to get to the other side.
Energy in Chemical Reactions
For a chemical reaction to occur three conditions have to be met as stated by the collision theory: 1. The reactants must come in contact with each other. 2. The reactants must be in the proper orientation to break old bonds and form new bonds. 3. The reactants must collide with enough force to produce the required energy to break the old bonds so new bonds can form.
Identify which element is oxidized and which element is reduced in the following equation: 2NaI + Br2 → 2NaBr + I2
I is oxidized, Br is reduced
Exothermic Reaction
In an exothermic reaction, energy is released such that the energy level of the products is lower than the initial energy level of the reactants. **Since the products are at a lower energy level than the reactants, the difference will be a negative ΔH value.** This means that energy, usually in the form of heat, is produced when the reactants are turned into products so energy is like a product formed during the reaction.
The catalyst is not a reactant or a product and is not changed during the chemical reaction.
It facilitates the formation of products by lowering the activation energy of the reaction
The Law of Conservation of Mass
Matter is not created nor destroyed in any chemical or physical change
Identify which element is oxidized and which element is reduced in the following equation: Mg + Cl2 → MgCl2
Mg is oxidized, Cl is reduced
Which example below is NOT a characteristic of an endothermic process?
Negative ΔH value & the beaker feels hot to touch during a chemical reaction.
Reaction Speed
Reactions can happen slow or fast. EX of Slow: Iron and Oxygen forming rust on a doorknob EX of Fast: Combustion reaction with match and fire
Identify the type of reaction: Mg + 2HCl → MgCl2 + H2
Single replacement
Redox Reactions
When there is a transfer of one or more electrons from one reactant to another. Oxidation-reduction reactions are commonly referred to as redox reactions
Single Placement Reaction (a.k.a. displacement reaction)
a reaction in which one element takes the place of another element in a compound The single element reactant will replace the element it is most like in the compound meaning a metal with replace a metal and a nonmetal will replace a nonmetal.
Combustion Reactions occur when .......
carbon-containing compounds react with oxygen to form carbon dioxide, water and heat. The carbon-containing compounds are usually hydrocarbons which contain only carbon and hydrogen atoms.
Identify the type of reaction: 2HgO → 2Hg + O2
decomposition
When temperature lowers:
decreasing the temperature reduces the rate of the reaction because the molecules are moving slower. The reactants will be less likely to exceed the activation energy required to form products when they are moving slowly.
Endothermic Reaction
energy is absorbed such that the energy level of the products is higher than the initial energy level of the reactants. The heat of the reaction is the difference between the energy level of the products and the energy level of the reactants which is designated as Δ H. **Since the products are at a higher energy level than the reactants, the difference will be a positive Δ H value**
Reduction takes place when an element gains electrons so the charge of the element will decrease or become more negative: .........
gain electrons reduced (GER).
Chemical reaction
is a process in which a chemical change occurs. the original substance, reactant, is changed into a new substance, product, with a different chemical formula and new properties.
Oxidation takes place when an element loses electrons so the charge of the element will increase or become more positive: .....
lose electrons oxidized (LEO)
Increasing the amount of reactant will result in ...........
more collisions that form product thus increasing the rate of the reaction.
Decreasing the amount of react will .......
slow the reaction rate because fewer collisions will occur and less product will be formed.
The rate of a chemical reaction can be affected by factors such as .........
temperature, amount of reactant and the presence of a catalyst.
Double Replacement Reaction (a.k.a. metathesis reactions)
two compounds react to form two new compounds. This is achieved by switching the positive ions of the two ionic compounds to form two new compounds
