Download 19-Oct

Draw and describe the following molecule:
Chemistry 6A F2007
8 + 4×(2)
Dr. J.A. Mack
= 16 electrons needed
5 + 4×(1) − 1 = 8 electrons needed
16 − 8
= 8 electrons shared
4 bonds
N must go into the
center since H can
only have one bond
H
N
remove one for the
charge!
Tetrahedral shape!
+
H
10/19/07
NH +4
H
H
10/19/07
Dr. Mack. CSUS
1
What is the net ionic equation for the reaction of aqueous lithium
hydroxide and aqueous nitric acid?
H
H
N
H
Dr. Mack. CSUS
2
Which of the following chemical equations is an acid-base reaction?
Molecular Equation:
a) 2 HCl(aq) + Zn(s) → H2(g) + ZnCl2(aq)
b) HCl(aq) + NH3(aq) → NH4Cl(aq)
LiOH(aq) + HNO3(aq) → H2O(l) + LiNO3(aq)
balanced?
yes!
Ionic Equation:
c) HCl(aq) + AgNO3(aq) → AgCl(s) + HNO3(aq)
d) Ba(OH)2(aq) + Na2SO4(aq) → BaSO4(s) + 2 NaOH(aq)
e) 2 NaOH(aq) + CuCl2(aq) → Cu(OH)2(s) + 2 NaCl(aq)
Li+(aq) + OH−(aq) + H+(aq) + NO3− (aq) →
Net Ionic Equation:
If you chose “b” you are correct!
H2O(l) + Li+(aq) + NO3− (aq)
a) is a RedOx reaction and c) to e) are precipitation reactions!
OH−(aq) + H+(aq) → H2O(l)
10/19/07
10/19/07
+
H
Dr. Mack. CSUS
3
10/19/07
Dr. Mack. CSUS
4
1
Which species in the reaction below undergoes reduction?
All of the following are oxidation-reduction reactions EXCEPT
Sn(s) + 2 H+(aq) → Sn2+(aq) + H2(g)
0
+1
+2
+2, −2
0
+1, −2
+2, −2, +1
a) CaO(s) + H2O(l) → Ca(OH)2(aq)
b) H2(g) + Br2(g) → 2 HBr(g)
c) Ca(s) + 2 HCl(aq) → CaCl2(aq) + H2(g)
What is the oxidation number of phosphorus in P2O5?
d) 2 NaBr(aq) + F2(g) → 2 NaF(aq) + Br2(g)
O = −2
10 ÷ 2 = +5
P2O5
e) 2 H2O(l) → 2 H2(g) + O2(g)
5×(−2) = −10
If you chose “a” you are correct!
P = +5
10/19/07
Dr. Mack. CSUS
5
Predict the products of the following reactions:
+ Cl2(g)
→
MgCl2(s)
6
All chemical processes are accompanied by energy changes:
balanced?
Yep!
If a reaction gives off energy (heat
heat), it is an exothermic reaction.
Solutions of nitric acid and sodium carbonate are mixed…
Reactants
2 HNO3(aq) + Na2CO3(aq) → H2O(l) + CO2(g) + 2 NaNO3(aq)
balanced?
Which is an acid neutralization reaction?
Dr. Mack. CSUS
Energy and Chemical Reactions
magnesium metal reacts with chlorine gas to form…
Mg(s)
10/19/07
Nope!
Products
+
Energy
If a reaction absorbs energy (heat
heat), it is an endothermic reaction.
Energy
+
Reactants
Products
Energy can be treated as part of the reactants or products!
products
10/19/07
Dr. Mack. CSUS
7
10/19/07
Dr. Mack. CSUS
8
2
Thermochemical Equations:
Energy and Chemical Reactions
Reactants
E (Products)
Energy
When the reaction is reversed , the sign of ∆H reverses:
Products
E (Reactants)
∆ERXN > 0
∆ERXN < 0
E (Reactants)
E (Products)
When the products are
higher in energy than the
reactants, the rxn is:
When the products are
lower in energy than the
reactants, the rxn is:
9
The amounts of substances and heat are expressed per
moles.
1 mole
+ Cl2(g) → 2HCl(g)
1 mole
CO2(g) + 2H2O(g) → CH4(g) + 2O2(g)
∆H = + 802 kJ
Endothermic
Dr. Mack. CSUS
H2(g)
∆H = − 802 kJ
Exothermic
Exothermic
Endothermic
10/19/07
CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)
+ 185 kJ
10/19/07
10/19/07
They are the numbers in front of the chemical
formulas.
2 mole
They give the ratio of reactants and products.
1mol H 2
185kJ
103 J
×
×
= 2.17 × 106 J
2.02g H 2 1mol H 2 1kJ
Dr. Mack. CSUS
11
Stoichiometric balancing coefficients
How many kJ of energy are released when 23.7 g of
hydrogen are reacted with excess chlorine to form hydrogen
chloride.
23.7g H 2 ×
Dr. Mack. CSUS
Conversion
factors
ratio
The balancing coefficients allow us to convert between
numbers of reactants and products.
12
10/19/07
Dr. Mack. CSUS
13
3
Since the individual ratios must scale to moles, we can
write:
Stoichiometry: The branch of chemistry that deals with
the mole proportions of chemical reactions.
Stoichiometric ratio: The ratio of any two species
(reactants or products) in a balanced chemical reaction.
2A + 3B
A2B3
2A
2 mols A
3B
3 mols B
The molar ratios allow us to relate the amounts of reactants
and products in a chemical equation.
2 A’s combine with 3B’s
CONVERSION FACTORS!!!
2A
3B
3B
10/19/07
i.e.
14
Consider the following reaction:
10/19/07
= 2 mols A
3 mols B
2 mol
3 H2(g)
+ N2(g)
16
2 NH3(g)
Write all of the molar ratio conversion factors for this reaction:
how many should there be?
1 mol N 2
3 mol H 2
Dr. Mack. CSUS
15
ammonia is formed from its elements:
N2(g) + 3H2(g) → 2NH3(g)
3 mol
Dr. Mack. CSUS
Consider the following reaction:
ammonia is formed from its elements:
10/19/07
2 mols A
2A
Dr. Mack. CSUS
1 mol
3 mols B ×
10/19/07
six… 3 × 2
3mol H 2
1mol N 2
1mol N 2
2mol NH 3
3mol H 2
2mol NH 3
1mol N 2
3mol H 2
2mol NH 3
1mol N 2
2mol NH 3
3mol H 2
Dr. Mack. CSUS
17
4
Give the following reaction
Given the following reaction, how many moles of
nitrogen are needed to completely react 9 moles of
hydrogen?
3 H2(g)
9 mol H2
+ N2(g)
1mol N 2
3mol H 2
×
2C2H6 (g) + 7 O2(g)
3 mol of N2
10/19/07
×
Dr. Mack. CSUS
4CO2(g) + 6H2O(l)
How many moles of water are produced when 3 mols of oxygen react?
2 NH3(g)
3.0 mol O 2 ×
= 3 mol of N2
2 sig. figs.
How many mols of ammonia will be produced?
2mol NH 3
1mol N 2
→
6 mol H 2O
7 mol O 2
exact
conversion
factor
= 2.6mol H 2O
2 sig. figs.
How many moles of C2H6 must react to produce 1.75 mols of CO2?
= 6 mol NH3
1.75 mol CO2 ×
18
10/19/07
2 mol C2 H 6
= 0.875 mol C2H6
4 mol CO 2
Dr. Mack. CSUS
19
5