A Chemical Reaction occurs when the of a substance changes.

Transcription

1 Perid: Unit 8 Chemical Reactin- Guided Ntes Chemical Reactins A Chemical Reactin ccurs when the f a substance changes. Chemical Reactin: ne r mre substances are changed int ne r mre new substances by the f cmpnent. Hw d Chemical Reactins Occur? The describes the cnditins fr a reactin t ccur The cllisin thery states that (atms r mlecules) must fr a chemical reactin t ccur Evidence f a Chemical Reactin is prduced A (a slid) is frmed Odr/gas is released - bubbling frm a gas being prduced and/r a is prduced Heat is is prduced change alng with anther change The f the prducts are different frm the reactants What Evidence f a Chemical Reactin d yu see? 1

2 Perid: Chemical Equatins : A representatin f a chemical reactin using the frmulas f the starting substances that react and the new substances that are frmed : the starting substances that enter int a chemical reactin ( side f the reactin arrw) : the new substances frmed during a chemical reactin ( side f the reactin arrw) : yields r a reactin arrw; separates reactants and prducts X + Y XY; are reactants is the prduct Signs and Symbls Symbl Meaning States f Matter Cefficients: Number f a substance; apply t in cmpund/mlecule Subscripts: number an element; applies t element (g), (l), (s):,, (aq): (disslved in water) Law f Cnservatin f Mass is neither created nr destryed in a chemical reactin The starting mass f = the final mass f Must be satisfied when describing a reactin (satisfied by ) 2

3 Perid: Atms are rearranged Same f each element n bth sides f the reactin arrw : Shw amunt f each substance. In frnt f a cmpund. Apply t all elements in the cmpund. are used t balance SUBSCRIPTS CAN NEVER BE CHANGED!!! H 2O: Hydrgen atms and Oxygen atm 2 H 2O : Hydrgens and Oxygen atms Cefficients shw f: Frmula units r mlecules invlved Relative amunts expressed in mles Balancing Chemical Reactins In rder fr an equatin t reflect the Law f Cnservatin f Mass it must be. The # f f each element n the reactants side must the # f f each element n the prducts side. A balanced equatin has the same number f atms n sides f the equatin. Tips t Remember: NEVER CHANGE THE when balancing an equatin Must use whle-number cefficients (n ) N cefficient means If yu get stuck, multiple cefficients by and start ver (cmbustin ONLY) 1) Write CORRECT frmulas fr the reactant and prduct. Remember the 7 diatmic gases (H 2, Br 2, O 2 N 2, Cl 2, I 2, F 2) 2) Balance the number f atms n bth sides by adding cefficients. DO NOT change the subscripts!!!! Useful tips t try: Make an inventry Rewrite water as Balance as a grup if appear n bth sides f the equatin 3

4 Perid: Balance and last Ex. MgCl 2 + H 2O Mg(OH) 2 + HCl Practice: Aluminum sulfate reacts with barium chlride t frm aluminum chlride and barium sulfate. Nitrgen gas plus hydrgen gas under pressure and at high temperature turn int ammnia. 5 Types f Chemical Reactins: - ccurs when different cmpunds react t frm new cmpunds. - ccurs when an element replaces an element that is part f a cmpund. - ccurs when simple substances cmbine t frm mre cmplex substance. - ccurs when cmplex substance breaks dwn int simpler substances - a type f displacement reactin where a cmpund is reacted/burned with gas t prduce,, and Why are Reactin Types Imprtant? Mst reactins will fit int ne f the five types. (There are.) Scientist use the types f reactins t. Being able t write a chemical equatin des nt necessarily mean that the reactin will actually take place. #1 Duble Displacement Reactins different cmpunds react t frm new cmpunds Als called duble General frmula: AX + BY AY + BX Duble displacement reactins: f the prducts frmed must be: 4

5 Perid: A (a slid) A (water r will be indicated liquid) A ( r will be indicated gas) reactin: a special type f displacement reactin in which an reacts with a t prduce a and. Examples: Ca(OH) 2 (aq) + 2HCl (aq) CaCl 2 (aq) + 2H 2O(l) 2NaOH(aq) + CuCl 2(aq) 2NaCl (aq) + Cu(OH) 2 (s) In each f the reactins ne f the prducts is a,, r a. Slubility: S slid- a slid that readily disslves in water (aq) slid- a slid that disslves t such a small degree that it is nt detectable t the naked eye (s) - An insluble slid that frms during a chemical reactin (will lk r lk like a ) (s) Slubility Rules: A set f rules/guidelines that indicate whether a substance will be in water ( ) r whether it will be in water ( ) Lcated n the back f yur peridic table Knw hw t use them Sluble r Insluble? Sdium Sulfate Calcium acetate Fe(OH) 2 AlPO 4 LiOH PbSO 4 Duble Displacement Practice: Write and balance the chemical equatin fr the fllwing reactins. Indicating state f matter. If the reactin will nt take place, write NR (fr n reactin) after the reactin arrw. Barium hydrxide reacts with hydrchlric acid t prduce barium chlride and water. 5

6 Perid: Phsphric acid reacts with ammnium hydrxide t prduce ammnium phsphate and water. Sdium chlride reacts with lithium brmide t frm sdium brmide and lithium chlride. #2 Single Displacement Reactins An element r a mlecule replaces an element that is part f a cmpund Als called single replacement General frmula: A + BX AX + B will replace and will replace What type f ins d metals frm? What type f ins d nn-metals frm? Requirements: fllw the : Arrangement f elements rganized in the rder f ease with which they underg certain chemical reactins Used t predict prducts fr single displacement reactins nly There are different activity series activity series activity series Elements can replace any element it n the activity series, but NOT any element it Activity decreases as yu mve the grup Metals n the list will replace metals n the list. A metal lwer n the list will nt replace a metal abve it n the list; in this case we write fr n reactin The farther 2 elements are n the series, the mre likely the higher ne will replace the lwer ne in a cmpund. Examples: Cpper metal reacts with silver nitrate t frm silver and cpper nitrate Lithium metal reacts with water t frm lithium hydrxide and hydrgen gas 6

7 Perid: Practice: Reactin r N Reactin? Ag (s) + Cu(NO 3) 2 (aq) F 2(g) + 2NaBr(aq) Br 2(g) + NaF(aq) 2 BN(s) + 3 F 2(g) #3 Synthesis Reactins Occurs when r mre simple substances cmbine t frm substance that is mre cmplex. D nt wrry abut states f matter General frmula is A + B AB Examples: 2 Fe + 3 Cl 2 2 FeCl 3 2 Na + Cl 2 2 NaCl Practice: Write the cmplete balanced chemical equatin fr the fllwing synthesis reactins: Cpper metal reacts with xygen gas t frm cpper (II) xide Aluminum metal reacts with xygen gas t frm aluminum xide Calcium metal reacts with nitrgen gas t frm calcium nitride Slid sulfur (S 8) reacts with xygen gas t frm sulfur dixide #4 Decmpsitin Reactins A cmplex substance breaks dwn int r mre simpler substances General frmula: AB A + B D nt wrry abut states f matter Examples: Ammnium nitrate decmpses t frm dinitrgen mnxide and water NH 4NO 3 N 2O + 2H 2O Sdium nitride decmpses t frm sdium metal and nitrgen gas 2NaN 3 2 Na + 3 N 2 7

8 Perid: Practice: Write the cmplete balanced chemical equatin (including states f matter) fr the fllwing synthesis reactins: Water decmpses int hydrgen gas and xygen gas Slid sdium chlride decmpses int sdium metal and chlrine gas Liquid ammnia decmpses int nitrgen gas and hydrgen gas #5 Cmbustin Reactins A type f reactin in which hydrcarbns (substances made f,, and smetimes ) are burned in t prduce and All reactants and prducts are in the state r state General frmula: C xh y (l) + O 2 (g) CO 2 (g) + H 2O (l) Examples: CH 4(l) + 2O 2(g) CO 2(g) + 2H 2O(l) 2C 2H 6(l) + 7O 2 (g) 4CO 2 (g) + 6H 2O(l) Practice: Balance the fllwing. Remember Balance hydrgen and xygen last and if yu get stuck, multiple cefficients by 2 and start ver (cmbustin ONLY) CH 4(g) + O 2(g) H 2O (g) + CO 2(g) C 12H 26(g) + O 2(g) H 2O (g) + CO 2(g) C 3H 8(g) + O 2(g) H 2O (g) + CO 2(g) 8