chemistry module 4

• Chemical reactions involve bonds being broken and formed as atoms rearrange to make new substances.
• A chemical reaction starts with a reactant (the initial substance before a chemical change) and ends with a product (the new substance created after a chemical change).
• Chemical reactions are often represented using chemical equations.
• Chemical equations describe the substances that react and the products that are produced.
• Chemical equations are read from left to right.
• The reacting substances are to the left of an arrow, and the newly formed products are to the right of an arrow.
• The phase of matter of each substance are sometimes shown in subscripts: (s) for solid, (l) for liquid, and (g) for gas.
• Compounds that have been dissolved in water to form a solution are given the subscript (aq) for aqueous solution.
• Chemical equations focus on the components of a chemical equation.
• One of the most important principles of chemistry is the law of conservation of mass, which states that matter is neither created nor destroyed during an ordinary chemical reaction.
• In a chemical reaction, all the atoms that were present at the beginning of the reaction are present at the end of the reaction, they have just been rearranged to bond differently and form new substances.
• Chemical equations represent the law of conservation of mass by always having equal numbers of each element on both sides of the equation, this is known as "balanced".
• The chemical equation showing the formation of water looks like this: H (pictured as two grey spheres attached by a rod) plus O (pictured as two larger red spheres attached by a rod) yields H O (pictured as one large red sphere attached to two grey spheres, each by a single rod).
• In a chemical reaction, atoms cannot be created or destroyed, they can only be rearranged.
• The chemical equation needs to be balanced by changing the number of joined hydrogen atoms on the reactant side to 2H (pictured as two molecules made with two grey spheres attached by a rod) plus O yields 2H O (pictured as two molecules made with one large red sphere attached to two grey spheres, each by a single rod).
• The number 2 in front of the joined hydrogen atoms on the reactant side of this equation shows how many of these joint diatomic molecules are necessary for the chemical reaction to take place.
• The law of conservation of mass states that the mass of all the reactants will always add up to the total mass of all the products.
• synthesis reaction is when two or more reactants combine to form one product
• decomposition reaction is when a single compound is broken down into two or more simpler compounds
• synthesis occurs with elements, compounds, or polyatomic ions
• decomposition occurs with compounds made from elements or polyatomic ions
• electrolysis is a process that uses electricity to decompose a substance
• combustion reaction is a compound/element that reacts with oxygen and creates light and heat
• exothermic is a chemical/physical change that releases energy into the environment
• combustion reactions always involve molecular oxygen as a reactant
• anything that burns is a combustion reaction
• organic combustion compounds contain carbon covalently bonded with other elements
• when a hydrocarbon combusts, the products are usually h2o and co2
• synthesis reactions can be combustion reactions because a substance can react with oxygen and release oxygen, but this only applies to inorganic compounds
• synthesis reaction formula = a+b > ab
• decomposition reaction formula = ab > a+b
• double replacement reaction formula = ab + cd > ad + cb
• single replacement reaction formula = a + bc > ac + b
• combustion (organic) reaction formula = CxHx + O2 > H2O + CO2
• combustion (inorganic) = A + O2 > AOx
• redox reaction formula = A (loses electron) + B (gains electron). A is oxidized and B is reduced
• in a single displacement reaction, the reactant is always an element and a compound
• in single displacement reactions, the products are always a different element and a different compound
• in double replacement reactions, the reactants are always two compounds
• in double replacement reactions, the products are always two different compounds