Thermochemical Equations

A thermochemical equation is a stoichiometric question that now involves the variable of ΔHReaction. Instead of doing a mole to mole comparison we will now do a mole to ΔH comparison. 

Enthalpy and Chemical Reactions

Concept: Understanding Thermochemical Equations

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Video Transcript

Welcome back, guys. In this new video, we're going to take the concepts we learned about thermal chemistry and apply it to an older concept, stoichiometry.
Now, what we had to learn about the stoichiometric chart, we're going to have to continue to apply here. But now we're going to incorporate delta H of reactions. We're going to say a thermal chemical equation is an equation, a balanced equation, that contains our heat of reaction that's just delta H of reaction. 

Example: Iron is reacts with oxygen according to the following equation at around 2000oC.  (0:35 – 4:10)

4 Fe (s)  +  3 O­2 (g)  → 2 Fe2O3 (s)         

ΔHo = + 65.2 kJ/mol

Calculate the amount of grams of iron (III) oxide, Fe2O3, produced from the absorption of 4.82 x 109 J. 

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Problem: Nitromethane (CH3NO2), sometimes used as a fuel for drag racing, burns according to the following reaction: 4 CH3NO2 (l) + 7 O2 (g) -----> 4 CO2 (g) + 6 H2O (g) + 4 NO2 (g) ?H = ? 2441.6 kJ How much heat is released by burning 125.0 g of nitromethane (MW: 61.044 g/mol)?

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Thermochemical Equations Additional Practice Problems

Consider the process of 2 H(g H2(g) where ΔH = −436 kJ/mol

Determine if the sentence below is true or false.

Reacting two moles of H(g) would release 436 kJ.

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Consider the process of 2 H(g H2(g) where ΔH = −436 kJ/mol

Determine if the sentence below is true or false.

Reacting two moles of H(g) would produce 2.02 grams of H2

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In an exothermic chemical reaction:

A + 2 B → C

When the amount of A and B reacting is doubled, what is expected to the amount of heat released?

 

A. No change in the amount of heat released

B. The amount of heat released is two times the original

C. The amount of heat released is four times the original

D. The amount of heat released is eight times the original

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Given the chemical reaction:

C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g)                 ΔH = −2044 kJ

How much energy would be released if 2.0 moles of O 2 were reacted?

A. 8.2 * 10 2 kJ

B. 2.1 * 10 3 kJ

C. 4.1 * 10 3 kJ

D. 2.0 * 10 4 kJ

E. 1.3 * 10 5 kJ

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What mass and volume of benzene (C6H6, d= 0.88 g/mL, molar mass = 78.11 g/mol) is required to produce 3.3 x 108 kJ of heat according to the following reaction?

2 C6H(l) + 15 O (g)   →   12 CO (g) + 6 H2O (g)          ΔH°rxn = – 6278 kJ

 

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What mass of water would need to evaporate from your skin in order to dissipate 1.7 x 105 J of heat from your body?

H2O(l) → H2O(g)           ΔH vap = 40.7 kJ/mol

 

A) 7.52 x 104 g

B) 418 g

C) 75.2 g

D) 58.4 g

E) 6.92 x 106 g

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A large part of the driving force in a thermite reaction is based on the stability of aluminum oxide, as reflected in ΔH° of the following reaction:

2Al (s) + 3/2 O(g) → Al2O(s) ΔH° =  - 1669.8 kJ/mol

 

If 27 g of aluminum reacts with oxygen to form Al 2O3(s), how much heat is released assuming the reaction goes to completion?

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Given the chemical reaction: C + 2 H 2 → CH4 has a ΔH = −74.9 kJ how much energy in kJ changes if 35.0 g of H2 is reacted?

A) −218        

B) −649          

C) −1.30 x 103          

D) −2620          

E) −5240

 

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Given the following:

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