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.

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