# Calculate which of two reaction is more exothermic

Which reaction is more exothermic?

A reaction with Keq=500 or a reaction with Keq=0.002?

https://brainmass.com/chemistry/energetics-and-thermodynamics/calculate-which-of-two-reaction-is-more-exothermic-1659

#### Solution Preview

(Please refer to the attached file, as the formatting of Greek letters, etc. in this HTML version may be jumbled.)

To answer this question, you will need the following equations, as well as an understanding of some basic thermodynamic concepts. You should be familiar with these equations from your lectures. If not, they will be available in your textbook. EXAM TIPS: When exam time comes, ...

#### Solution Summary

In addition to a full answer, this problem solution provides an explanation of how to approach deciding which reaction is more exothermic, when you have a limited amount of information. The problem only provided the Keq values, without stating other experimental conditions (such as temperature or reaction components). This creates a challenging and tricky situation for the student -- you will need to understand thermodynamic equations and relationships, and use that understanding to reason (rather than calculate) which of the two reactions is more exothermic. Exam tips for this type of problem are also shown in the html version of the solution (but not in the attachment).

Gas Laws & Heat Of Reaction

1.

For the reaction

2 NO(g) + O2(g) -->2 NO2(g)

deltaH = -126.0 kJ at 25C.

(a) Calculate the amount of heat transferred when 333 g of NO(g) reacts with O2(g) at 25C and 1 atm.

(b) Does this heat flow into the system or does it flow to the surroundings?

(c) Is this reaction exothermic or endothermic?

2.

If 8675 J of heat flows into 135.0 g of water initially at 20.0C, find the final temperature of

the water. The specific heat of water is 4.18 J g^-1 K^-1.

3.

Find the molecular weight of a gas if 22.24 g of the gas in a 7045 cm^3

container at 20°C exerts a pressure of 698 torr.

CONSTANTS

R = 0.08206 L atm mol^-1 K^-1

1 atm = 760 torr

c = 3.00 x 10^8 m/s

h = 6.63 x 10^-34 J . s

4.

Calculate deltaH at 25C is -1790 kJ for the reaction

C3H6O(l) + 4O2(g) -->3 CO2(g) + 3 H2O(l)

Given these f deltaH values at 25C: -394 kJ/mol for CO2(g), -286 kJ/mol for H2O(l), and 0 for

O2(g), find f deltaH for C3H6O(l).

5.

What volume of H2(g) at 27C and 1.08 atm is produced when

45.3 g of Al reacts as follows:

2Al + 6HNO3(aq) --> 2Al(NO3)3 + 3H2

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