Chemical Reactions A chemical reaction is a process by which substances are formed into new substances. The substances that you begin with, and undergo change are called reactants. The substances that you end with, which are formed as a result of the chemical reaction, are called products. So, during a chemical reaction, reactants are changed into products.

Chemical Equations A chemical equation represents a chemical reaction through writing the reactants and products as formulas. Ex: 2C + 2O2 2CO2 Coefficient Reactants Products

Balancing Equations The law of conservation of matter states that mass is neither created nor destroyed in a chemical reaction. So, the mass of the reactants MUST equal the mass of the products…..the number of atoms of each of the elements on the right side of the equations must equal the number of atoms of each of the elements on the left. C + O2 CO2 = 1 C and 2 O atoms on each side

Balancing Equations If the equation is not balanced, you can balance it by changing the coefficients, which are the numbers in front of the formulas. THIS IS THE ONLY NUMBER YOU CAN CHANGE!!!! The coefficient is multiplied times the subscript to find the total number of atoms of an element. Ex: 2H2O = 4 H atoms and 2 O atoms Bozeman - Balancing Equations https://m.youtube.com/watch?v=_B735turDoM

Balancing Equations Practice: Reactants: Fe, O2 Product: FeO Products: N2, O2 Reactants: N2O4 CH4 and O2 react to form CO2 and H2O

Energy of Reactions All chemical reactions release or absorb energy. The source of the energy is the chemical bonds – Breaking chemical bonds releases energy. Most chemical reactions require energy in the form of activation energy to break the bonds of the reactants. Forming chemical bonds requires energy. When more energy is released than absorbed, the reaction is said to be exergonic (energy exiting); if the energy takes the form of heat, it is exothermic. Most energy used in homes and industry is exogonic. When more energy is absorbed than released, it is said to be endogonic; if the energy takes the form of heat, it is endothermic.

Energy of Reactions The law of conservation of energy states that energy cannot be created or destroyed, it can simply change form. In a reaction, energy is often shown as a product or a reactant. The total amount of energy before and after the reaction must remain the same. Ex: CH4 + 2O2 CO2 + 2H2O + energy Is this reaction endogonic or exergonic?

Types of Reactions There are several types of reactions – some general types: Synthesis Decomposition Single-replacement Double-replacement Combustion

Types of Reactions A synthesis reaction is one in which two or more substances react to form one substance. The general equation for a synthesis reaction is A + B AB The reactants in a synthesis reaction may be elements or compounds. The product must be a compound.

Types of Reactions A decomposition reaction is the opposite of a synthesis reaction – a compound breaks down into two or more simpler substances The general equation for a decomposition reaction is AB A + B The reactant in a decomposition reaction must be a compound. The products may be elements or compounds. Bozeman Science https://m.youtube.com/watch?v=yS8noHTIJ_E

Types of Reactions A single-replacement reaction is one in which one element takes the place of another element in the compound. The general equation for this reaction is A + BC B + AC

Types of Reactions A double-replacement reaction is one in which two different compounds trade positive ions and form two new compounds. The general equation for this reaction is AB + CD AD + CB

Types of Reactions A combustion reaction is one in which a substances reacts with oxygen, often producing energy as heat and light.

Types of Reactions Reactions in which electrons are transferred from one reactant to another is called an oxidation- reduction reaction, or redox reaction.

Types of Reactions Any process in which an element LOSES electrons during a chemical reaction is called oxidation – a reactant is oxidized if it loses an electron. The process in which an element GAINS electrons during a chemical reactions is called a reduction – a reactant is said to be reduced if it gains electrons. OIL RIG Oxidation is Loss Reduction is Gain https://m.youtube.com/watch?v=lQ6FBA1HM3s (First 2-3 minutes)

Reaction Rate Any change that happens over time can be expressed as a rate. A reaction rate is the rate at which reactants change into products. Chemical reactions involve collisions between particles of reactants. Anything that causes those collisions to occur more frequently, will cause the reaction rate to increase.

Reaction Rate Factors that affect reaction rates include Temperature Surface area Concentration Stirring Catalysts How would increasing each of these affect reaction rates? https://www.youtube.com/watch?v=OttRV5ykP7A#t=23

Reaction Rate A catalyst is a substance that affects the reaction rate without being used up during a reaction. An inhibitor does the opposite – it slows the reaction rate of a reaction, without being used up. http://youtu.be/KYD5LNVWne8

Equilibrium Equilibrium is a state in which the forward and reverse paths of a change take place at the same rate. When opposing physical changes take place at the same rate, a physical equilibrium is reached. Ice water at 0ºC – if the temperature remains at 0ºC, then any water that freezes would be balanced by ice melting (why?) When opposing chemical changes take place at the same rate, a chemical equilibrium is reached.

Equilibrium Most chemical reactions are reversible to some extent… reversible reactions are reactions in which the reactions can change into products, and the products can change into reactants at the same time. When a chemical reaction does not go to completion, a chemical equilibrium is established between the forward and reverse reactions.

Equilibrium Chemical equilibria can change, depending on the conditions of the reaction. When a change is introduced, the equilibrium shifts in the direction that relieves the change – this rule is known as Le Chatelier’s Principle. Crash Course Chem - equilibrium http://youtu.be/g5wNg_dKsYY