Heat/Q/systems
Enthalpy graph drawn by Mrs. Onushko.
Label
-Activation Energy
-Endo or Exothermic
-What is more stable: Reactants or Products
Grade as a class
Qx = mx * cx * (delta)Tx
Fill in every x for finding the energy released by a potato chip
x can = chip or water
Name the products of a hydrocarbon (CxHyOz) complete combustion reaction.
Name the 2 types of products for incomplete combustion. WHEN does incomplete combustion happen (what situations).
Complete: CO2 and H2O
Incomplete: When limited O2 available
CO + H2O
C + H2O
A reaction has a (Delta)H = -273
If you needed to flip that equation and multiply the coefficients by 3, what would the new (Delta)H =?
Flip means - goes to +
multiplying the equation by 3 means you need to multiply 273 by 3
(delta)H = +819
Na+ (aq) + e- --> Na(s)
2Cl- (aq)--> Cl2 (g) + 2e-
What 1/2 reaction is oxidation? What 1/2 reaction is reduction?
Ox: Chlorine
Red: Sodium
Mrs. Onushko will draw an enthalpy graph with numbers. Calculate (delta)H for the reaction.
corrected in class
If water absorbed 350 kJ of heat, the potato chip that burned absorbed/released _ kJ of heat.
-/+ # kJ
released 350 kJ of heat.
-350 kJ from the chip
balance this combustion reaction
__ C3H8 + __O2 --> __CO2 + __ H2O
1 5 3 4
2N2 + 5 O2 → 2N2O5 ΔH = ?
H2 + ½O2 → H2O ΔH = -285.8
N2O5 + H2O → 2HNO3 ΔH = -76.6
N2 + 3O2 + H2 → 2HNO3 ΔH = -348.2
Reaction 1: flip x2 +571.6
Reaction 2: flip, x2 +153.3
Reaction 3: x2 -696.4
28.4
What are the oxidation numbers of every atom?
Al(OH)3 SbF61-
Al = +3 O = -2 H = +1
Sb = +5 F = -1
How many Calories is 84000 joules?
How many calories is 600 kilojoules?
20.1 J
143403 cal
Ethanol was burned. It started out as 10 g and ended at 7 g. There was 50 mL water in the calorimeter. The water started out at 20C and ended at 25C.
How much energy (J) did the water absorb?
1046 J
Define the term average bond enthalpy
Energy required to break 1 mole of a bond in a gaseous molecule averaged over similar values.
"Old" IB chem book - page 192, #4
describe what you would do to the equations
Reaction 1: Leave it
Reaction 2: flip
(don't erase your board, use for next question)
Write the 1/2 reactions:
SeO32- + I- --> I2 + Se
(no need to balance or do e-)
SeO3 --> Se
I- --> I2
Save for next question
Mrs. Onushko sets up an experiment in a plastic bag. When the reactants mix, she feels the bag. One observation recorded is that it feels cold. Is this mystery reaction endothermic or exothermic?
feels cold means the system (the reaction) is stealing my heat. It is gaining heat. the system is going through a endothermic reaction.
The surroundings would be considered Mrs. Onushko
Ethanol was burned. It started out as 10 g and ended at 7 g. There was 50 mL water in the calorimeter. The water started out at 20C and ended at 25C.
How much energy per gram did the ethanol release? (J/g)
348.67 J/g
C2H2 + 2H2 --> C2H6
Using this and the given Lewis structures, use page 11 to calculate the enthalpy change using bond enthalpy data
-291 kJ
"Old" IB chem book - page 192, #4
What is the enthalpy, in kJ, of the reaction?
Reaction 1: Leave it stays -144
Reaction 2: flip +11 flipped to -11
-144 + -11 = -155
SeO32- + I- --> I2 + Se
Balance. Which 1/2 reaction is ox? Which 1/2 reaction is red?
Red: 4e- + 6 H+ + SeO32- --> Se + 3H2O
Ox: 2I- --> I2 + 2e- (mult by 2)
Final: 4I- + 6 H+ + SeO32- --> Se + 3H2O + 2I2
Mrs. Onushko burns ethanol C2H5OH in a watch glass. She puts a lid on over the burning watch glass to collect the products.
1) What are the products?
2) Is this an open or a closed system?
CO2 and H2O
Closed System- No oxygen in/out, products cannot get in/out.
A piece of metal was in boiling water (100) and cooled to room temp (20C). If the metal was 60 g and it released 8760 J of energy in the process, what is the metal?
Be
sugar (C6H12O6) combusts. Write a balanced combustion reaction.
(complete combustion)
C6H12O6 + 6O2 --> 6CO6 + 6 H2O
2N2 + 5 O2 → 2N2O5 ΔH = ?
H2 + ½O2 → H2O ΔH = -285.8
N2O5 + H2O → 2HNO3 ΔH = -76.6
N2 + 3O2 + H2 → 2HNO3 ΔH = -348.2
Reaction 1: flip x2 +571.6
Reaction 2: flip, x2 +153.3
Reaction 3: x2 -696.4
28.4
Balance this redox reaction
Cr2O72- + HNO2 --> Cr3+ + NO3-
6e + 14H+ + Cr2O72- --> 2Cr3+ + 7H2O
HNO2 + H2O --> 3H+ + NO3- + 2e- (mulp by 3)
Final: 3HNO2 + 5H+ + Cr2O72- --> 3NO3- + 2Cr3+ + 4H2O