CHAPTER 11: CHEMICAL REACTIONS Mrs. Brayfield
WRITING EQUATIONS Write the chemical equation for the following: Magnesium metal reacts with hydrochloric acid to form aqueous magnesium chloride and hydrogen gas Mg s + HCl aq MgCl 2 aq + H 2 (g) Sulfur burns in oxygen to form sulfur dioxide S s + O 2 (g) SO 2 (g)
CHEMICAL REACTIONS What is a chemical reaction? It is where one or more things changes What are examples of chemical reactions? How can we describe what happens in chemical reactions? Reactants Products
CHEMICAL EQUATIONS A chemical equation is a representation of a chemical reaction For example the reaction between iron and oxygen: Fe + O 2 Fe 2 O 3 A skeleton equation is a chemical equation that does not indicate the relative amounts of the reactants and products
SYMBOLS IN CHEMICAL EQUATIONS (on page 348)
BALANCING CHEMICAL EQUATIONS When we look at the skeletal equation for a bike: F + 1W + H + 1P FW 2 HP 2 We don t see the relative amounts of each part. This is called an unbalanced equation
BALANCING CHEMICAL REACTIONS The balanced equation for a bike would be: F + 2W + H + 2P FW 2 HP 2 The balanced equation is where each side of the equation has the same number of atoms of each element
BALANCING CHEMICAL EQUATIONS F + 2W + H + 2P FW 2 HP 2 The small whole numbers in front of the formulas to balance the equation are called the coefficients
BALANCING CHEMICAL REACTIONS So there are three steps when balancing chemical reactions: 1. Write the skeleton equation 2. Use coefficients to balance the equation 3. Make sure that there are the same number of atoms of each element on both sides of the equation
BALANCING CHEMICAL REACTIONS The following reactions are balanced: C(s) Carbon + O 2 (g) Oxygen CO 2 (g) Carbon dioxide
TYPES OF REACTIONS In Chemistry we can classify reactions into five general types: 1. Combination Reaction 2. Decomposition Reaction 3. Single-Replacement Reaction 4. Double-Replacement Reaction 5. Combustion Reaction
COMBINATION (OR SYNTHESIS) REACTION A combination reaction is where two or more substances react to form a single new substance + Chemical example: 2Mg s + O 2 (g) 2MgO(s)
DECOMPOSITION REACTION A decomposition reaction is where a single compound breaks down into two or more simpler products (the opposite of combination reactions) + Chemical example: 2NaN 3 s 2Na s + 3N 2 (g)
SINGLE REPLACEMENT REACTION A single replacement reaction is where one element replaces a second element in a compound + + Chemical example: Zn s + Cu(NO 3 ) 2 aq Cu s + Zn(NO 3 ) 2 (aq)
DOUBLE REPLACEMENT REACTIONS A double replacement reaction involves an exchange of positive ions between two compounds + + Chemical example: FeS s + 2HCl aq FeCl 2 s + H 2 S(g)
COMBUSTION A combustion reaction is where an element or compound (fuel) reacts with oxygen to form carbon dioxide and water The fuel is typically a hydrocarbon (compound containing carbon and hydrogen)
COMPLETE AND NET IONIC EQUATIONS Sometimes in chemical equations we are only interested in the gases, liquids, and solids that form The way that we can do this is by looking at the complete ionic equation and the net ionic equation
COMPLETE IONIC EQUATION The complete ionic equation shows dissolved ionic compounds as dissociated free ions If given the chemical equation of: AgNO 3 aq + NaCl aq AgCl s + NaNO 3 (aq) The complete ionic equation would be: Ag + aq + NO 3 aq + Na + aq + Cl aq AgCl s + Na + aq + NO 3 aq
COMPLETE IONIC EQUATION Notice that the nitrate ion and the sodium ion appear on both sides of the equation We can simplifying the equation by eliminating these ions because they do not participate in the reaction Ag + aq + NO 3 aq + Na + aq + Cl aq AgCl s + Na + aq + NO 3 aq
NET IONIC EQUATION When we simplify the equation and have only the species undergoing the reaction, we have the net ionic equation: Ag + aq + Cl aq AgCl s The ions that we cancelled are the ones that are not directly involved in the reaction. These ions are called spectator ions NO 3 aq, ina + aq
NET IONIC EQUATIONS So the net ionic equation shows us what is actually happening in the chemical reaction ONLY single replacement and double replacement reactions can be written as net ionic equations
PREDICTING THE FORMATION OF A SOLID During a chemical reaction if there a solid formed, we call that solid the precipitate This solid precipitates out of solution because it is insoluble in water (cannot be dissolved) How can we tell if we formed a solid? We use some general rules for solubility
SOLUBILITY RULES (on page 372)
PREDICTING PRODUCTS Using all of our knowledge about the 5 types of reactions, we can predict the products of reactions using these steps: 1. Determine what kind of reaction the reactants will most likely form 2. Look at the solubility rules to determine if a solid formed 3. Balance the chemical reaction
PREDICTING PRODUCTS So if we have the following reactants: KI aq, ipbno 3 aq What would be the products? Well, this is a double replacement reaction so KI aq + PbNO 3 aq PbI? + KNO 3 (? ) Did we form any solids? YES! KI aq + PbNO 3 aq PbI s + KNO 3 (aq)