Chemical reactions

Agenda Bell Work

• Draw both the Bohr model and the Lewis dot model of the following:– Aluminum– Carbon– Arsenic– Argon– helium

• Atoms and the Periodic table Jeopardy

• Notes: Chemical Equations and Reactions

• Molecular models

• Model and Change Quiz tomorrow

Chemical Equations and Chemical Equations and ReactionsReactions

April 2, 2013April 2, 2013

ObjectivesObjectives

1.1. Explain the difference between elemental Explain the difference between elemental and chemical formulaand chemical formula

2.2. Recognize all the parts of a chemical Recognize all the parts of a chemical equationequation

3.3. Describe how compounds are different Describe how compounds are different than the materials that compose itthan the materials that compose it

4.4. Balance Chemical EquationsBalance Chemical Equations

Chemical BondingChemical Bonding

The attraction between two atoms that The attraction between two atoms that holds them togetherholds them together

Chemical changes occur because of breaking and Chemical changes occur because of breaking and rearrangementrearrangement

Chemical change = chemical reactionChemical change = chemical reaction

Chemical EquationChemical Equation

To show chemical reactions we use To show chemical reactions we use chemical equationschemical equations

C + OC + O22 --> CO --> CO22

44 Al Al (s)(s) + + 33 OO2 (g)2 (g) ---> ---> 22 AlAl22OO3 (s)3 (s)

Parts of Chemical EquationParts of Chemical Equation

Elemental formula:Elemental formula: how atoms are how atoms are bounded together in an elementbounded together in an element LiLi OO22 , N , N22 , S , S88

Chemical formula:Chemical formula: representation representation of a compound, when atoms of of a compound, when atoms of different elements bond to each otherdifferent elements bond to each other NaCl, NHNaCl, NH3 3 , CO, CO22

Subscript:Subscript: represents how represents how many of a many of a particular atomparticular atom

Coefficient:Coefficient: represents how represents how many of a many of a particular element particular element or moleculeor molecule

(s) represents solid

(l) represents liquid

(g) represents gas

(aq) represents aqueous

How many atoms?How many atoms?

C + OC + O22 --> CO --> CO22

44 Al Al (s)(s) + + 33 OO2 (g)2 (g) ---> ---> 22 AlAl22OO3 (s)3 (s)

Chemical EquationChemical Equation

Reactants --> ProductsReactants --> Products

C + OC + O22 --> CO --> CO22

when reading an equation Arrow = yieldswhen reading an equation Arrow = yields

Law of Conservation of MassLaw of Conservation of Mass

Matter is neither created nor destroyed Matter is neither created nor destroyed during a chemical reactionduring a chemical reaction

Therefore all chemical equations must be Therefore all chemical equations must be balanced; equal atoms of each element on balanced; equal atoms of each element on each sideeach side

Balancing equation rulesBalancing equation rules

You may change the coefficients in frontYou may change the coefficients in front

You may NOT change the subscriptsYou may NOT change the subscripts

Changing the subscript changes the Changing the subscript changes the compoundcompound

Steps of balancingSteps of balancing

1.1. Write the correct formulas for the Write the correct formulas for the equation. Once written do not change equation. Once written do not change the formula’sthe formula’s

2.2. Find the number of atoms on the left side Find the number of atoms on the left side of each element and compare it against of each element and compare it against the number of atoms of the same the number of atoms of the same elements on the right sideelements on the right side

4. 4. Check your answer to see if:Check your answer to see if: The numbers of atoms on both The numbers of atoms on both

sides of the equation are now sides of the equation are now balanced.balanced.

The coefficients are in the lowest The coefficients are in the lowest possible whole number ratios. possible whole number ratios. (reduced)(reduced)

Helpful hintsHelpful hints

Take one element at a time working left to Take one element at a time working left to right,right,

Leave H for next to last and O lastLeave H for next to last and O last

IF everything balances except for O, and IF everything balances except for O, and there is no way to balance O with a whole there is no way to balance O with a whole number, double all the coefficients and try number, double all the coefficients and try again.again.

Balancing EquationsBalancing Equations___ H___ H22(g) + ___ O(g) + ___ O22(g) ---> ___ H(g) ---> ___ H22O(l)O(l)

One of the oxygen atoms One of the oxygen atoms

binds with two of the binds with two of the

hydrogen atomshydrogen atoms

Done ActivitiesDone ActivitiesWhich equations are balanced?Which equations are balanced?

Balance the ones that aren’tBalance the ones that aren’t

a.Mg(s) + 2HCl(aq) a.Mg(s) + 2HCl(aq) MgCl MgCl22(aq) + H(aq) + H22(g)(g)

b. Al(s) + Brb. Al(s) + Br22(l) (l) Al Al22BrBr66(s)(s)

c. HgO(s) c. HgO(s) Hg(l) + O Hg(l) + O22(g)(g)

___ Al(s) + ___ Br___ Al(s) + ___ Br22(l) ---> ___ Al(l) ---> ___ Al22BrBr66(s)(s)

____C____C33HH88(g) + _____ O(g) + _____ O22(g) ---->(g) ---->

_____CO_____CO22(g) + _____ H(g) + _____ H22O(g)O(g)

____B____B44HH1010(g) + _____ O(g) + _____ O22(g) ---->(g) ---->

_____B_____B22OO33(g) + _____ H(g) + _____ H22O(g)O(g)