Created by C. Ippolito Dec 2006 Chemical Reactions Objectives: 1. interpret the information in chemical equations. 2. balance chemical equations and relate this process to the law of conservation of mass 3. classify chemical reactions as belonging to one of four types 4. predict products of single and double replacement reactions.

Created by C. Ippolito Dec 2006 Chemical Reactions ssubstances change their identity one or more substances are used up to form one of more new substances RRRReactants substances that exist before the change (starting materials) PPPProducts substances that exist after the change (materials produced)

Created by C. Ippolito Dec 2006 Word Equations ddescribes the reaction using the names of substances silver + sulfur  silver sulfide ““silver reacts with sulfur to yield silver sulfide” glucose + oxygen  carbon dioxide and water ““glucose reacts with oxygen to yield carbon dioxide and water RRRReactants – before the “arrow” PPPProducts – are after the “arrow”

Created by C. Ippolito Dec 2006 Formula Equations ddescribes a chemical reaction using the formulas of the reactants and products 2Mg + O 2  2MgO CCCCoefficients numbers in front of formulas indicate relative number of formula units (ionic substances) or molecules (covalent substances) or atoms (elements) BBBBalanced Equation illustrates law of conservation of mass ssame number of atoms and types of atoms on BOTH SIDES 2Mg + O 2  2MgO 2Mg2Mg 2O2O

Created by C. Ippolito Dec 2006 Balancing Equations HH 2 + O 2  H 2 O tally atoms: aatoms H: 2  2 aatoms O: 2  1 change coefficient to balance O atoms HH 2 + O 2  2H 2 O tally atoms: aatoms H: 2  4 aatoms O: 2  2 change coefficient to balance H atoms 22H 2 + O 2  2H 2 O tally atoms: aatoms H: 4  4 aatoms O: 2  2 equation is balanced

Created by C. Ippolito Dec 2006 Balancing Another Equation ZZn + HCl  ZnCl 2 + H 2 tally atoms: aatoms Zn: 1  1 aatoms H: 1  2 aatoms Cl: 1  2 change coefficient to balance H atoms ZZn + 2HCl  ZnCl 2 + H 2 tally atoms: aatoms Zn: 1  1 aatoms H: 2  2 aatoms Cl: 2  2 equation is balanced

Created by C. Ippolito Dec 2006 Balancing Yet Another Equation HH 2 SO 4 + NaOH  H 2 O + Na 2 SO 4 tally atoms: aatoms H: 3  2 aatoms S: 1  1 aatoms Na: 1  2 aatoms O: 5  5 change coefficient to balance Na atoms HH 2 SO 4 + 2NaOH  H 2 O + Na 2 SO 4 tally atoms: aatoms H: 4  2 aatoms S: 1  1 aatoms Na: 2  2 aatoms O: 6  5 change coefficient to balance O atoms

Created by C. Ippolito Dec 2006 Balancing (con’t) HH 2 SO 4 + 2NaOH  2H 2 O + Na 2 SO 4 tally atoms: aatoms H: 4  4 aatoms S: 1  1 aatoms Na: 2  2 aatoms O: 6  6 equation is balanced

Created by C. Ippolito Dec 2006 Energy Changes in Equations EEEEndothermic Reactions energy with reactants energy put into cause reaction (before the arrow) 22H 2 O + energy  2H 2 + O 2 EEEExothermic Reactions energy with products (after the arrow) energy released from reaction (after the arrow) 22H 2 + O 2  2H 2 O + energy

Created by C. Ippolito Dec 2006 Phases in Equations ssolid – (s) lliquid – (l) ggas – (g) aaqueous solution – (aq) ttincture – (al) 2HCl(aq) + Zn(s)  ZnCl 2 (aq) + H 2 (g)

Created by C. Ippolito Dec 2006 Classifying Chemical Reactions Types of Chemical Reactions Direct Combination (synthesis) Decomposition(analysis) Single Replacement Double Replacement (exchange of ions)

Created by C. Ippolito Dec 2006 Direct Combination ttwo or more substances or elements combine to form a single more complex substance A + B  AB 22H 2 (g) + O 2 (g)  2H 2 O(l) 22CO(g) + O 2 (g)  2CO 2 (g) CCaO(s) + H 2 O(l)  Ca(OH) 2 (s)

Created by C. Ippolito Dec 2006 Decomposition aa single substance is broken down into two or more simpler substances (endothermic) energy from heat or electricity catalyst – speeds up reactions without being changed 22H 2 O(l)  2H 2 (g) + O 2 (g)

Created by C. Ippolito Dec 2006 Single Replacement Reactions aa free element replaces an ion in a solution causing the ion to be come a free element A + CD  C + AD not all elements can do only more reactive elements can replace less reactive elements (use Activity Series - Table J) Zn(s) + H 2 SO 4 (aq)  ZnSO 4 (aq) + H 2 (g) Cu(s) + 2AgNO 3 (aq)  2Ag(s) + Cu(NO 3 ) 2 (aq) Cl 2 (g) + 2NaBr(aq)  Br 2 (l) + 2NaCl(aq).

Created by C. Ippolito Dec 2006 Double Replacement Reactions iinvolves two ionic compounds in aqueous solutions tthe cation of one ionic compound replaces the cation the other ionic compound AB + CD  AD + CB not all ionic solutions will do this mmust be insoluble – form a precipitate rreplacement forms water rreplacement forms a gas AgNO 3 (aq) + NaCl(aq)  AgCl(s) + NaNO 3 (aq) NaOH(aq) +HCl(aq)  NaCl(aq) + H 2 O(l) NH 4 Cl(aq) + NaOH(aq)  NH 4 OH(aq) + NaCl(aq)  NH 3 (g) + H 2 O(l) + NaCl(aq).