11.1 - Describing Chemical Reactions

reactants yield products

l - liquid

g - gas

q - aqueous solution (dissolves in water)

s - solid

word equations - write names of the reactants on the left and the products on the right

hydrogen + sulfur → hydrogen sulfide

H(sub. 2) + S → H(sub. 2)S

chemical equation (aka skeletal) - shorthand method that represents a chemical reaction by using formulas of the reactants on the left and the products on the right

a catalyst can be added to a reaction

• catalyst - any substance that speeds up a chemical reaction but not used up in the reactants — usually written above arrow

SYMBOLS

• a plus sign separates 2 reactants/products

• an arrow means “yields”

• a back and forth arrow means that the reaction is reversible

• a triangle over an arrow means that heat is supplied to the reaction

• an element over an arrow means that the element is used as a catalyst

to balance an equation, change the coefficient, NOT the subscripts

coefficients - small whole numbers placed in front of the formula to balance the equation

balanced equation - must contain same number of atoms and elements in the reactants as the products

Zn + HCl → ZnCl + H(sub. 2)

2Zn + 2HCl → 2ZnCl + H(sub. 2)

to write a balanced equation

• write skeleton equation

• use coefficients

11.2 - Types of Chemical Reactions

• synthesis

  • A + B → AB

  • chem chg in which 2 or more substances react to form a single new substance

• decomposition

  • AB → A + B

  • chem chg in which a single compound breaks down into 2 or more simpler products

• single-replacement

  • AB + C → A + CB

  • chem chg in which 1 element replaces a 2nd element in a compound

whether one metal will displace another from a compound depends upon relative reactivities of the 2 metals

activity series - lists metals in order of decreasing reactivity

reactivity of halogens decrease as you go down 7A — a halogen can replace a halogen

• double-replacement

  • AB + CD → CB + AD

  • chem chg involving an exchange of positive ions between 2 compounds

• combustion

  • chem chg in which an element or a compound reacts with oxygen, often producing energy in the form of heat and light

  • a compound of carbon/hydrogen and oxygen are usually the reactants

  • CO2 and H2O are usually the products

the number of elements and/or compounds reacting is a good indicator of possible reaction type and thus possible products

note fig. 11.10 pg 338-339

11.3 - Reactions in Aqueous Solutions

dissociated

• taking ionic compounds and temporarily separating them

• not a chem chg, but is a physical chg (dissolving)

complete ionic equation - an equation that shows dissolved ionic compounds as dissociated free ions

spectator ion - and ion that appears on both sides of an equation and is not directly involved in the reaction

net ion equation - equation for a reaction in solution that shows only the particles that are directly involved in the chem chg and are balanced with respect to mass and charge