CHEMICAL REACTIONS Basics

OBJECTIVES

CHEMICAL REACTIONS  All Chemical reactions have a few things in common  They all start with the reactants  They all end with the products  The total mass at the beginning is equal to the total mass at the end (law of conservation of __?____)  If I start with 10g of O at the beginning, then I will have 10g of O at the end

 In English, we use sentences to explain what is happening  In chemistry, we use equations to explain what is happening as well.  This reads “Reactants yield (or produce) products.”

 Say that I wanted to say that iron reacts with oxygen to make rust.  I could say just that  But I could just as easily say Iron + Oxygen  Iron (III) Oxide Iron + Oxygen  Iron (III) Oxide (not balanced)  Oxidation state (charge from valence electrons)  Use a + sign when you have more than one compound

 Say that I wanted to say that hydrogen peroxide decomposes into water and oxygen.  I could say just that  But I could just as easily say Hydrogen Peroxide  water + oxygen (not balanced) Hydrogen Peroxide  water + oxygen (not balanced)

 Say that I wanted to say that methane and oxygen combine to form water and carbon dioxide (word equation)  I could say just that  But I could just as easily say Methane + oxygen  water + carbon dioxide (not balanced) (Skeleton Equation) Methane + oxygen  water + carbon dioxide (not balanced) (Skeleton Equation)

 This a skeleton equation. It does not balance the equation or tell us any ratios  Fe+ O 2  Fe 2 O 3  H 2 O 2  H 2 O + O 2  CH 4 (g) + O 2 (g)  CO 2 (g) + H 2 O (l)  The letters in parentheses tell what state the compound is in at the time.  (aq) refers to a solution with water as the solvent

OBJECTIVES

 Though we can use skeleton equations to express what is happening in simpler terms, chemical equations give us details that we can use to determine actual amounts.  4 Fe+ 3 O 2  2 Fe 2 O 3  2 H 2 O 2  2 H 2 O + O 2  CH O 2  CO 2 + 2H 2 O

 In an unbalanced equation, we can see all the products and reactants.  But we do not know how many of each that we need.  That would be like making a cake without knowing how many eggs, how much sugar, etc. was needed to make it right.  A balanced equation tells us exactly what ratio of ingredients we need in order to get the cake we want.

1. Write the skeleton equation 2. Compare the number of each atom in the reactants to the number of the same atom in the product 3. Pick one of the unequal atoms and multiply the compound by a number so that the atoms are equal on each side. (This number is called the coefficient) 1. Fe 2 O 3 + H 2  Fe + H 2 O 2. Fe 2  1 1. O 3  1 2. H 2  2 3.Fe 2 O 3 + H 2  2Fe + H 2 O

4. Repeat steps 2 and 3 until the equation is balanced 5. Done 6. The balanced equation tells us the ratio (based upon the coefficients) for each compound in the products and reactants. 4. In the example to the right, for every 1 Iron oxide molecule 3 hydrogen molecules are required. 5. This also means 2 molecules of iron and 3 molecules of water are produced. 1. Fe 2 O 3 + H 2  Fe + H 2 O 2. Fe 2  1 1. O 3  1 2. H 2  2 3.Fe 2 O 3 + H 2  2Fe + H 2 O 4. Fe 2  2 1. O 3  1 2. H 2  2 5.Fe 2 O 3 + H 2  2Fe + 3H 2 O 6. Fe 2  2 1.O 3  3 2. H 2  6 7.Fe 2 O 3 + 3H 2  2Fe + 3H 2 O 8. Fe 2  2 1. O 3  3 2. H 6  6

CLOSURE  What step in the process of balancing an equation gives you the most difficulty?

OBJECTIVES

CATALYSTS  A catalyst is anything that can accelerate a reaction without being used up  It is not a product or reactant so it is placed above the arrow when writing a chemical equation  This would be read as hydrogen peroxide in the presence of manganese (IV) oxide decomposes into water and oxygen

5 TYPES OF CHEMICAL REACTIONS

VOCABULARY  Combination reaction  A reaction in which 2 simple compounds combine to make 1 compound  Decomposition reaction  A reaction in which 1 (complex) compound is separated into different components  Single Replacement reaction  A reaction in which 2 compounds (1 simple & complex) react and one component on a compound is replaced by another

VOCABULARY  Double Replacement reaction  A reaction in which 2 (complex) compounds exchange components with each other  Combustion reaction  A reaction in which a compound reacts with oxygen  Activity Series  A table which shows the relative reactivity of various compounds. This helps determine which compounds would be replaced by another.

REACTION TYPE: COMBINATION  Normally this involves 2 elements combining to make a compound, but it is possible for two compounds to combine to make a new compound.  When a metal is combined with a non-metal, the result is an ionic compound (salt).

REACTION TYPE: COMBINATION When two non-metals are bonded, there can be multiple products. When a transition metal is combined with another element, multiple products are possible as well.

REACTION TYPE: COMBINATION

CHEMISTRY Today is the last day for food, drinks, or bathroom passes. Until you can clean up after yourselves so I don’t have to, it will remain this way.  Agenda –  Bellringer  Identifying 5 different reaction types  Predicting products for the different reaction types

REACTION TYPE: DECOMPOSITION It can sometimes be difficult to predict the products of a decomposition reaction, but when there are only 2 components to a compound, the simpler parts formed in the decomposition are apparent.

REACTION TYPE: DECOMPOSITION

 In a single replacement reaction, normally an element and a component of a compound exchange places.  Normally positive replaces positive, negative will replace negative REACTION TYPE: SINGLE REPLACEMENT In the case of water, many times only one H will be replaced leaving a hydroxide ion combined with the replacing element

 An activity series  helps us predict when one metal will replace another.  The element farther up the list will replace one lower on the list.  Also, a halogen can replace a different halogen only if it (the halogen to do the replacing) is above it (the halogen to be replaced) on the periodic table This reaction will happen, while the one below will not. REACTION TYPE: SINGLE REPLACEMENT

CHEMISTRY Bellringer, tell me what type of reaction is shown in each problem.Also, take 1 of the ten and work it out completely. Remember, keep it clean or no food, drink, or rr.  Agenda –  Bellringer  Identifying 5 different reaction types  Predicting products for the different reaction types

 A double replacement reaction is one in which two compounds exchange the components with positive charges.  They are sometimes called double-displacement reactions  They generally takes place in an aqueous solution  They will also often produce a precipitate (solid),a gas, or some molecular compound such as water. REACTION TYPE: DOUBLE REPLACEMENT

 There are some generalities that apply to double displacement reactions. One of the following is usually true. 1. One of the products is only slightly soluble (able to be dissolved) and precipitates 2. One of the products is a gas. 3. One of the products is a molecular compound like water. REACTION TYPE: DOUBLE REPLACEMENT

 A combustion reaction is a reaction in which an element or a compound reacts with oxygen, often producing light and heat  Oxygen is always a reactant.  Often a hydrocarbon (CH or their derivatives) is the other reactant  Methane, propane, butane, etc.  Though other elements will combine with oxygen  These reactions can often be classified as some of the other 4 types of reactions. REACTION TYPE: COMBUSTION REACTION

OBJECTIVES

NET IONIC EQUATIONS  This is the way that we have done balanced reactions so far  However, in aqueous solutions (in water) most ionic compounds dissociate (separate into cations and anions)  We can now show a complete ionic equation by showing each dissolved ionic compounds as being free ions.

NET IONIC EQUATIONS  Notice that the NO 3 - does not change. Since the nitrate ion and the sodium ion appear on both sides of the equation and they do not seem to do anything in this reaction, they are called a spectator ions. We will actually not even show them in the reaction.  This new equation is called a net ionic equation (net as in after everything that is not important is removed).

NET IONIC EQUATIONS  In the previous reaction, both sides of the equation are balanced (neutral on both sides)  In any net ionic equation the charge on the reactant side must equal the charge on the product side.  In this reaction, nitrate is the spectator ion again.

NET IONIC EQUATIONS  In this net ionic reaction, there is a +1 charge on the reactant side and a +2 charge on the product side. This is unacceptable.

PREDICTING A PRECIPITATE  A precipitate (ppt) is a solid that is sometimes formed when combining two non-solid reactants.  The only way to know if it will form a ppt is to look at its solubility.  If it is insoluble, then it will form a ppt.

PREDICTING A PRECIPITATE  For this we have to look at the chart to the left.  This should be a double displacement reaction forming sodium nitrate (soluble) and barium carbonate (insoluble)

PREDICTING A PRECIPITATE  This leaves us the above reaction as our net ionic reaction

PREDICTING A PRECIPITATE  A precipitate (ppt) is a solid that is sometimes formed when combining two non-solid reactants.  The only way to know if it will form a ppt is to look at its solubility.  If it is insoluble, then it will form a ppt.