Wize High School Grade 12 Chemistry Textbook > Energy Changes

Introduction to Thermochemistry
 What is thermochemistry?
   Thermochemistry is the study of the energy changes involved in chemical and physical processes            
 Chemical vs Physical Changes
A chemical change is when bonds are b roken and formed between different atoms
Ex. Burning a compound in a chemical reaction is an example of a chemical change. The compound is changed as a result of the burning and can't be changed back (we get a new compound!)
CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)  
 
A physical change does not involve the breaking and forming of bonds. Instead, these involve a change of state
Solid  ⇌  Liquid  ⇌  Gas 
Ex. When ice melts, we have liquid water. Ice is H2O(s) while water is H2O(l). The compound is still the same and could be frozen again to become ice again!  
   

Energy: the capacity to do work or transfer heat

Are the following changes physical or chemical changes? 
                

A Change to a Compound	Chemical or Physical Change (Enter answer as C or P)
Seeing bubbles during a reaction
Feeling heat on the outside of a beaker during a reaction
Boiling the compound
Seeing a precipitate form in solution
Seeing light given off of the compound during the reaction
Melting the compound
Seeing a new compound form during the reaction

I don't know

Extra Practice

Which of the following is an Intensive Property?

Gibbs Free Energy

The reaction of 
H2(g)+CO2(g)↔H2O(g)+CO(g) at 2000K KP=4.40H_{2(g)}+CO_{2(g)}\leftrightarrow H_2O_{(g)}+CO_{(g)}\ at\ 2000K\ K_P=4.40H2(g)​+CO2(g)​↔H2​O(g)​+CO(g)​ at 2000K KP​=4.40 
Calculate ΔG for this reaction

Thermochemistry: Temperature

The oxidation of NO is shown below. Using the provided thermodynamic data answer the following questions 
2 NO(g)+O2(g)→2 NO2)g)2\ NO_{(g)}+O_{2(g)}\rightarrow2\ NO_{2)g)}2 NO(g)​+O2(g)​→2 NO2)g)​
ΔHo=−57.1kJmol and ΔSo=−73Jmol at 298K\Delta H^o=-57.1\frac{kJ}{mol}\ \text{and}\ \Delta S^o=-73\frac{J}{mol}\ at\ 298KΔHo=−57.1molkJ​ and ΔSo=−73molJ​ at 298K

Thermochemistry: Gibbs Free Energy

The oxidation of NO is shown below. Using the provided thermodynamic data answer the following questions
2 NO(g)+O2(g)→2 NO2)g)2\ NO_{(g)}+O_{2(g)}\rightarrow2\ NO_{2)g)}2 NO(g)​+O2(g)​→2 NO2)g)​
ΔHo=−57.1kJmol and ΔSo=−73Jmol at 298K\Delta H^o=-57.1\frac{kJ}{mol}\ \text{and}\ \Delta S^o=-73\frac{J}{mol}\ at\ 298KΔHo=−57.1molkJ​ and ΔSo=−73molJ​ at 298K 

Thermochemistry: Equilibrium (Keq)

The Haber Bosch Process is an industrial process for “fixing” nitrogen, shown below.This process produces around 500 million tons of ammonia every year. Calculate Keq
   3 H2(g)+N2(g)→ 2 NH3(g)3\ H_{2(g)}+N_{2(g)}\rightarrow\ 2\ \text{NH}_{3(g)}3 H2(g)​+N2(g)​→ 2 NH3(g)​
ΔfGo(NH3)=−16.4 kJ/mol\Delta _fG^o(NH_3)=-16.4\ kJ/molΔf​Go(NH3​)=−16.4 kJ/mol

 Using the following data, calculate the standard entropy change for the reaction: 
2Al(s)+3ZnO(s)→Al2O3(s)+3Zn(s)2Al_{(s)}+3ZnO_{(s)}\to Al_2O_{3(s)} +3Zn_{(s)}2Al(s)​+3ZnO(s)​→Al2​O3(s)​+3Zn(s)​
 Report your answer in J/mol K to four significant figures.  Do not include units in the answer field.  

A spontaneous process:

 Which of the following statements regarding spontaneous changes is false? 

A freshly baked pie is placed near an open window to cool. Which of the following statements best describes this situation? 

Thermodynamics: Heat and Work

Consider the following balanced chemical equation for the combustion of propane, C3H8:
C3H8(g)+5O2(g)→4H2O(ℓ)+3CO2(g)q<0C_3H_8 (g) + 5 O_2      (g) → 4 H_2O (ℓ) + 3      CO_2 (g) \qquad q < 0C3​H8​(g)+5O2​(g)→4H2​O(ℓ)+3CO2​(g)q<0
Use this information to answer the next two questions. Choose one if the options inside the brackets

If a reaction is nonspontaneous at 298 K with a negative ΔHo, then the reaction is:  
Select all that apply

 The oxidation of NO is shown below. Using the provided thermodynamic data answer the following questions 
 2 NO(g)+O2(g)→2 NO2)g)2\ NO_{(g)}+O_{2(g)}\rightarrow2\ NO_{2)g)}2 NO(g)​+O2(g)​→2 NO2)g)​ 
 ΔHo=−57.1kJmol and ΔSo=−73Jmol at 298K\Delta H^o=-57.1\frac{kJ}{mol}\ \text{and}\ \Delta S^o=-73\frac{J}{mol}\ at\ 298KΔHo=−57.1molkJ​ and ΔSo=−73molJ​ at 298K 

The oxidation of NO is shown below. Using the provided thermodynamic data answer the following questions
 2 NO(g)+O2(g)→2 NO2)g)2\ NO_{(g)}+O_{2(g)}\rightarrow2\ NO_{2)g)}2 NO(g)​+O2(g)​→2 NO2)g)​ 
 ΔHo=−57.1kJmol and ΔSo=−73Jmol at 298K\Delta H^o=-57.1\frac{kJ}{mol}\ \text{and}\ \Delta S^o=-73\frac{J}{mol}\ at\ 298KΔHo=−57.1molkJ​ and ΔSo=−73molJ​ at 298K 

Find ΔG0 for the following reaction.
         CH4(g)+2 O2(g)→2 H2O(g)+CO2(g)\text{CH}_{4(g)}+2\ O_{2(g)}\rightarrow 2\ H_2O_{(g)}+\text{CO}_{2(g)}CH4(g)​+2 O2(g)​→2 H2​O(g)​+CO2(g)​

 Consider the following vaporization: 
CH3CH2OH(l)→CH3CH2OH(g)CH_3CH_2OH_{(l)}\to CH_3CH_2OH_{(g)}CH3​CH2​OH(l)​→CH3​CH2​OH(g)​
 If ∆Hvap = 39.3 kJ/mol and the boiling point of ethanol is 78.3°C, what is ΔS for the vaporization of 1.73 mols of ethanol at its boiling point? 

Predict the sign of the ΔH, ΔS,(+ or -) and identify when the following reactions are spontaneous at low temperature, high temperature, or all temperatures (low, high, all).  Use commas to write your answers ie. +,+,low
 For freezing of a popsicle: ΔH is ___________, ΔS is ___________. Reaction is spontaneous at ____________________ temperatures
 For evaporation of liquid water: ΔH is ___________, ΔS is ___________. Reaction is spontaneous at ____________________ temperatures

 Arrange the following compounds in order of increasing entropy, assuming 1 mol of each compound: 
Ar(g)Fe(s)CH3CH2CH3(g)HOCH2CH2CH2OH(l)Ar(g) \hspace{15pt}Fe(s)\hspace{15pt} CH_3CH_2CH_{3(g)} \hspace{15pt} HOCH_2CH_2CH_2OH_{(l)}Ar(g)Fe(s)CH3​CH2​CH3(g)​HOCH2​CH2​CH2​OH(l)​
Ar(g)Ar(g)Ar(g)

Calculate ΔSsys ΔSsurr and ΔSUniv for the combustion of hydrogen shown below (unbalanced). Is the process spontaneous?
        H2(g)+O2(g)→H2O(g)H_{2(g)}+O_{2(g)}\rightarrow H_2O_{(g)}H2(g)​+O2(g)​→H2​O(g)​
ΔHf0(H2O(g)) = -285.83 kJ/mol

Thermochemistry: Entropy Calculations

Using the ΔH0 of fusion for water 6.03 kJ/mol and the ΔS0 of fusion for water 22.1 J K-1 mol-1, calculate the ΔSuniv for ice melting at -10oC, 0oC and 10oC. Remember: the universe transfers heat in a reversible way.

Thermodynamics: Entropy Calculations

Using the following data, calculate the standard entropy of the reaction shown below. Enter your answer in units of J / (mol*K)
2 Al(s)+3 ZnO(s)→Al2O3(s)+3Zn(s)2\ Al_{(s)}+3\ ZnO_{(s)}\rightarrow Al_2O_{3(s)}+3Zn_{(s)}2 Al(s)​+3 ZnO(s)​→Al2​O3(s)​+3Zn(s)​
So(Al(s))=28.3 J mol−1K−1S^o(Al_{(s)})=28.3\ J\ mol^{-1}K^{-1}So(Al(s)​)=28.3 J mol−1K−1