HESS'S LAW
Goal: PCl5(g) → PCl3(g) + Cl2(g)|
P4(s) + 6Cl2(g) → 4PCl3(g) ΔH = -2439 kJ |
4PCl5(g) → P4(s) + 10Cl2(g) ΔH = 3438 kJ |
What is 249.8 kJ
The value of the ΔH for any reaction that can be written in steps equals the _____of the value of ΔH for each of the individual steps. Hint* (Hess's Law)
What is sum
Goal: 2C2H4O(l) + 2H2O(l) → 2C2H6O(l) + O2(g)| answer = 204.0 kJ|
C2H6O(l) + 3O2(g) → 2CO2(g) + 3H2O(l) ΔH = -685.5 kJ |
C2H4O(l) + 5/2O2(g) → 2CO2(g) + 2H2O(l) ΔH =_________|
What is -583.5 kJ
Is ΔH positive or negative in an exothermic reaction?
What is negative.
Draw our calorimeter from our lab last week.
Goal: 2CO2(g) + H2O(g) → C2H2(g) + 5/2O2(g)|
C2H2(g) + 2H2(g) → C2H6(g) ΔH =-94.5 kJ |
H2O(g) → H2(g) + 1/2O2 (g) ΔH =71.2 kJ |
C2H6(g) + 7/2O2(g) → 2CO2(g) + 3H2O(g) ΔH =-283 kJ|
What is 235 kJ
When an equation is reversed- the sign of ΔH must also be _________________.
What is reversed
Goal: N2(g) + 2O2(g) → 2NO2(g)|
N2(g) + 3H2(g) → 2NH3(g) ΔH = -115 kJ |
2NH3(g) + 4H2O(l) → 2NO2(g) + 7H2(g) ΔH = -142.5 kJ
| ________→ H2(g) + 1/2O2(g) ΔH = -43.7 kJ
What is H2O(l)
Name and draw an example of heat transfering from the universe to a system.
Teacher discretion.
What should a calorimeter be made from?
Something that does not conduct heat or electricity.
Goal: N2H4(l) + H2(g) → 2NH3(g)|
N2H4(l) + CH4O(l) → CH2O(g) + N2(g) + 3H2 (g) ΔH = -37 kJ |
N2(g) + 3H2(g) → 2NH3(g) ΔH = -46 kJ |
CH4O(l) → CH2O(g) + H2(g) ΔH = -65 kJ|
What is -18 kJ
If all coefficients of an equation are multiplied or divided by the same factor, the value of ΔH must also be ______________________.
What is multiplied or divided by the same factor
Goal: CO2(g) → C(s) + O2(g)|
H2O(l) → H2(g) + 1/2O2(g) ΔH = 643 kJ |
C2H6(g) → _______________ ΔH = 190.6 kJ |
2CO2(g) + 3H2O(l) → C2H6(g) + 7/2O2(g) ΔH= 3511.1 kJ|
What is 2C(s) + 3H2(g)
In an endothermic reaction, is heat gained or lost in the system? Draw a diagram to illustrate the transfer of energy in an exothermic reaction.
What is gained, reactants--> products
What is the function of a calorimeter?
Allow for a chemical reaction to be observed without releasing or allowing in any additional energy.
Goal: H2SO4(l) → SO3(g) + H2O(g)|
H2S(g) + 2O2(g) → H2SO4(l) ΔH = -235.5 kJ |
H2S(g) + 2O2(g) → SO3(g) + H2O(l) ΔH = -207 kJ |
H2O(l) → H2O(g) ΔH = 44 kJ |
What is 72 kJ
The enthaply of the universe is always ____________.
Constant
Goal: N2H4(l) + CH4O(l) → CH2O(g) + N2(g) + 3H2 (g)|
2NH3(g) → N2H4(l) + H2(g) ΔH = 22.5 kJ |
2NH3(g) → N2(g) + 3H2(g) ΔH = 57.5 kJ |
_________________________ ΔH = 81.2 kJ |
What is CH2O(g) + H2(g) → CH4O(l)
A sample of ethanol absorbs 23.4kJ of energy. The temperature increases from 5.6 degrees Celsius to 19.8 degrees Celsius. What is the mass of the sample if the specific heat capacity (C) of ethanol is 2.46 J/ (goC)?
Hint: Q=M x C x ∆T
What is 669.87 grams
In our calorimetry lab, what was the system and what was the surroundings?
system- HCl & Mg ribbon in calorimeter
surrounds- classroom
Goal: 1/2H2(g) + 1/2Cl2(g) → HCl(g)|
COCl2(g) + H2O(l) → CH2Cl2(l) + O2(g) ΔH = 47.5 kJ |
2HCl(g) + 1/2O2(g) → H2O(l) + Cl2(g) ΔH = 105 kJ |
CH2Cl2(l) + H2(g) + 3/2O2(g) → COCl2(g) + 2H2O(l) ΔH = -402.5 kJ|
What is -230 kJ
Define the 1st law of thermodynamics:
First Law of Thermodynamics = Law of Conservation of Energy (energy of the universe is constant)
Goal: HCl(g) + NaNO2(s) → HNO2(l) + NaCl(s)|
2NaCl(s) + H2O(l) → 2HCl(g) + Na2O(s) ΔH = 507 kJ|
NO(g) + NO2(g) + Na2O(s) → 2NaNO2(s) ΔH = -427 kJ|
NO(g) + NO2(g) → N2O(g) + O2(g) ΔH = -43 kJ|
______________________________ ΔH = 34 kJ |
What is 2HNO2(l) → N2O(g) + O2(g) + H2O(l)
H2SO4(aq) + 2NaOH(aq) --> Na2SO4 (aq) + 2H2O (l) + 114 kJ
Is this reaction exothermic or endothermic?
What is exothermic?
Was our calorimetry lab exothermic or endothermic? State one reason to support this claim.
Exothermic, system gave off heat