GEORGIA MILITARY COLLEGE

NATURAL SCIENCE DEPARTMENT

ONLINE CAMPUS

LABORATORY 5 THERMOCHEMISTRY: ENTHALPY AND ENTROPY OF A SPONTANOUS REACTION

NAME

STUDENT NUMBER

CLASS

PROFESSORS TITLE AND NAME

Introduction

As a roaring bonfire rages, it releases heat (energy) to the surrounding environment, while also producing gaseous products such as water vapor and carbon dioxide. When it releases heat to the environment, the systems enthalpy decreases, while that of the surrounding environment increases. At the same time, the gaseous products increase the particles in the system, causing disorder and a subsequent increase in entropy. A combustion reaction thus serves as an example of a spontaneous reaction. A spontaneous reaction is a chemical reaction characterized by the release of free energy (King, 2023). However, the change in free energy (?G) depends on the entropy and enthalpy changes taking place in the system as shown below:

?G = ?H - T ?S

Enthalpy (symbolized as ?H) is a measure of a systems heat content. A positive ?H value shows that the system is endothermic (gaining heat), while a negative value shows an exothermic system (one that loses heat to the surroundings). On the other hand, entropy (symbolized as ?S) is a measure of the degree of disorder in a system (King, 2023). A positive ?S value shows an increase in the amount of disorder in a system, while a negative value shows a decrease in the amount of disorder (King, 2023). ?G is always negative for a spontaneous reaction because of the release of free energy. However, depending on the nature of the reaction, ?H and ?S can be either negative or positive, while T, which is measured in Kelvin, is always positive. Thus, ?G can take on one of four possible outcomes as shown in table 1 below:

Table 1: Enthalpy and Entropy vs Spontaneous Process

?H

?S

?G

Negative

Positive

Always Negative (spontaneous) at all T

Positive

Positive

Positive (non-spontaneous) at lower T, negative (spontaneous) at higher T

Negative

Negative

Positive (non-spontaneous) at higher T, negative (spontaneous) at lower T

Positive

Negative

Always positive (non-spontaneous)

According to the Second Law of Thermodynamics, a chemical reaction is spontaneous if it causes an increase in entropy or the amount of disorder in the system (King, 2023). Generally, solids are less disordered than liquids because of their regular structure. At the same time, liquids are less disordered than gases because gaseous particles are constantly in a state of random motion (King, 2023).

Based on the above context, this laboratory seeks to realize the...

At this point, all the supplies needed for the lab are available.

Performing the Lab

iv) Select Empty 1000mL Erlenmeyer flask, 10mL pipette, and 0.2L foam cup from the Glassware tab in...

…system, and hence, the ?S is negative. The loss of thermal energy from the system causes it to be less disordered, leading to a negative ?S. From the lab findings, this report concludes that:

i) In an exothermic reaction, ?S is negative

ii) In an endothermic reaction, ?S is positive

Based on the data collected during the experiment, the ?H (q-heat) of the reaction, assuming specific heat capacity = 4.18J/goc and density of the solution is 1.00g/mL, can be calculated by:

?H (q) = mCs ?T)

Where m is mass, Cs is specific heat capacity, and ?T is change in temperature of the reaction mixture. From the experiment, the mass of the reaction mixture can be calculated by:

Mass (m) = density x volume

Mass (m) = 1.00g/mL x 20mL

Mass (m) = 20g

At the same time, ?T is given by (27.290c - 250c)

?T = -2.290c

Therefore,

q = 20 x 4.18 x (-2.29)

q = -191.44

Conclusion

This laboratory sought to enhance understanding of enthalpy, entropy, and spontaneity in chemical reactions and to explore the second law of thermodynamics by investigating the process of thermal energy transfer in chemical reactions. Enthalpy (symbolized as ?H) is a measure of a systems heat content, while entropy is a measure of the degree of disorder in a system. The experiment involved observing the temperature change in the synthesis of 10mL of reagent X and 10mL reagent Y. The lab findings indicate that the reaction was exothermic as it involved loss of heat from the system into the surrounding environment. Consequently, the loss of heat reduced disorder in the system, leading to a reduction in the systems entropy. Thus, the…