Chemical Reactions

Chemical Formulas and Equations Section 1 Chemical Formulas and Equations

Chemical Reactions A. Matter can change physically or chemically; a process that produces a chemical change is a chemical reaction

Chemical Equations B. A chemical equation is a shorthand form of what reactants are used and what products are formed in a chemical reaction 2H2 + O2 → H2O

Chemical Equations B.1. Some equations use words or chemical names to identify reactants and products B.2. Chemical formulas represent chemical names of substances in a chemical equation

Law of Conservation of Mass C. The mass of reactants and mass of products in a chemical reaction is always the same due to the law of conservation of mass

Balanced Equations D. Chemical equations are balanced when the number of atoms is the same on each side of the equation

Energy of Reactions E. Energy is released or absorbed during a chemical reaction 1. When reactions release energy (exothermic reactions), the products have bonds with less energy than those of the reactants

Exothermic reactions Bromine is the dark red liquid at the bottom. Bromine is quite volatile, and you can see orange bromine vapor in the top of the beaker. About ten seconds after adding some torn aluminum foil, things look more like this A little later … And then …

Energy of Reactions E2. When reactions absorb energy (endothermic reactions), the reactants are more stable and their bonds have less energy than those of the products

Endothermic reactions A. Ammonium thiocyanate is mixed with barium hydroxide. The mixture is stirred and the two solids react. A slush is formed because water is one of the products of the reaction. B. A drop of water is placed on a block of wood and the beaker is placed on the water drop. The reaction is endothermic, that is, it takes in heat. C. As a result, the bottom of the beaker becomes cold enough to freeze the water and stick to the wood.

Energy of Reactions E.3. Heat energy may be absorbed or released; the rate of heat release can be rapid or slow E.4. The word energy can be written in a chemical equation as a reactant or product

Rates of chemical reactions Section 2 Rates of chemical reactions

Rates of Chemical Reactions A. Different chemical reactions take different amounts of time. B. Activation energy- is the amount of energy required to start a chemical reaction

Rates of Chemical Reactions C. The rate of reaction measures how quickly a reactant is disappearing or how quickly a product is appearing. 1. Tells how quickly the amount of substance changes per unit of time 2. Importance in industry: the faster a product can be made, the lower the cost CaCO3(s) + 2HCl(aq) CaCl2(s) + H2O(l) + CO2(g)

Rates of Chemical Reactions 3. Temperature can change the rate of reaction 4. Concentration, the amount of a substance present in a specific volume, affects the rate of reaction 5. Particle size affects the speed of a reaction

Rates of Chemical Reactions D. An inhibitor is a substance that slows down the rate of a chemical reaction E. A catalyst is a substance that speeds up a chemical reaction; enzymes are special protein molecules that act as catalysts in the body.

Synthesis and Decomposition Reactions These are two of the major types of chemical reactions. You can use their names to help you describe them: Synthesis means “to make”. From two or more reactants you create one product. Decomposition means “to break down”. You take one reactant and break it down into two or more parts. Sulfur reacting to heat.

A + B = C Synthesis reactions In a synthesis reaction- two or more simple substances combine to form a more complex substance. Another way to identify a synthesis reaction is two or more reactants yielding one product. For example, simple hydrogen gas combined with simple oxygen gas can produce a more complex substance-----water! 2H2 + O2 → H2O

Synthesis reactions The chemical equation for this synthesis reaction looks like: reactant + reactant -------> product To visualize a synthesis reaction look at the following cartoon: In the cartoon, the skinny bird (reactant) and the worm (reactant) combine to make one product, a fat bird.

Decomposition reactions A = B + C In a decomposition reaction a more complex substance breaks down into its more simple parts. One reactant yields 2 or more products. For example, water can be broken down into hydrogen gas and oxygen gas. 2H20 → 2H2 + O2 Basically, synthesis and decomposition reactions are opposites.

Decomposition reactions The chemical equation for this decomposition reaction looks like: reactant -------> product + product To visualize a decomposition reaction look at the following cartoon: In this cartoon the egg (the reactant), which contained the turtle at one time, now has opened and the turtle (product) and egg shell (product) are now two separate substances.