Chemical Reactions Types of Reactions
Types of Reactions • Combination reactions • Decomposition reactions • Displacement reactions • Precipitation reactions You need to be able to identify each type.
A. Combination • the combination of 2 or more substances to form a compound • only one product forms A+ BAB 2P + 3Br2 2PBr3
B. Decomposition • a compound breaks down into 2 or more simpler substances • only one reactant ABA+B 2H2O2 2H2O + O2
C. Displacement • one element replaces another in a compound • metal replaces metal (+) • nonmetal replaces nonmetal (-) A +BCAC+B Zn + 2HCl ZnCl2 + H2
D. Precipitation • ions in two compounds “change partners” • cation(+) of one compound combines with anion(-) of the other AB +CDAD +CB 2KOH + CuSO4 K2SO4 + Cu(OH)2
Exchange Reactions • Think about it like “foil”ing in algebra, first and last ions go together + inside ions go together • Example: AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq) • Another example: K2SO4(aq) + Ba(NO3)2(aq) KNO3(aq) + BaSO4(s) 2
Predicting the products • 1) Identify the likely reaction type based on the reactants: • Combination - often 2 elements • Decomposition - 1 compound • Displacement - 1 compound & 1 element • Precipitation - 2 compounds
Predicting the products • 2) Use the information in your notes about likely products to help you determine the products • Combination- put the 2 elements together-look at the charges and use the crisscross method • Decomposition- pull the compound apart- for us, it will usually be the 2 elements that make up the compound • Pay attention to the diatomics
Predicting Products • 2) continued • Displacement- look at the activity series to see if the element can replace one of the elements in the compound • If the reaction occurs, find the charges of the each of the elements. • Trade the places of the metals • Write the new formula of the compound using the crisscross method • Eliminate the charge from the new lone element and write it alone.
Predicting products • 2) Continued • Exchange - trade the cations of the compounds • Pay attention to charge of your ions and use the crisscross method to write the formula. • Look at your solubility table on the back of your periodic table to determine which product is solid (the insoluble one is the solid) and which is aqueous • Be sure to indicate state of matter for every compound in exchange reactions • If both are aqueous (soluble), no reaction occurs. • Water is a liquid
Predicting Products • 3) Balance the equation.
Practicing exchange reactions • Predict the products. • HCl(aq) + AgNO3(aq) • Pb(NO3)2(aq) + BaCl2(aq) • FeCl3(aq) + NaOH(aq) • KOH(aq) + CuSO4(aq) AgCl(s)+ HNO3(aq) PbCl2(s)+Ba(NO3)2(aq) 3 3 Fe(OH)3(s) + NaCl(aq) 2 K2SO4(aq) + Cu(OH)2(s)
Mixed Practice • State the type & predict the products. • BaCl2 (aq)+ H2SO4(aq) • Zn(s) + CuSO4(aq) • Cs(s) + Br2 (l) • FeCO3(s)
Exchange reaction 2 BaSO4(s) + HCl(aq) BaCl2(aq) +H2SO4(aq) • What you would see: • Two solutions are mixed and a white solid (precipitate) forms on mixing
Displacement reaction ZnSO4(aq) + Cu(s) Zn(s) + CuSO4(aq) • What you would see: • Copper sulfate solution fades in colour…gets less blue • Zinc metal disappears as it reacts • Brown/orange copper metal appears
Combination reaction 2 2 CsBr(s) Cs(s) + Br2 (l) • What you would see: • Explosion…lots of energy given off …Cs is a group one metal! • Brown/red bromine liquid would disappear quickly as it reacts • Silvery Cs metal would quicklydisappear as it reacts • A white crystalline solid is left behind
Decomposition reaction • FeCO3(s) FeO (s) + CO2(g) • What you would see: • You would need to heat this for the reaction to take place • green powder turns black • gas given off could be bubbled through limewater to test for carbon dioxide