Consider the following equation: 2C2H2(g) + 5O2(g) ->4CO2(g) + 2H2O(g) + energy (a) Does the equation represent an endothermic reaction or an exothermic reaction? (b) What effect would this reaction have on the temperature of its surroundings? Compare the temperature of the surroundings before the reaction takes place to the temperature of the surroundings after the reaction takes place. (c) What does the equation communicate about the relative energy of the chemical bonds in the reactants and products?
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
Consider the following equation:
2C2H2(g) + 5O2(g) ->4CO2(g) + 2H2O(g) + energy
(a) Does the equation represent an endothermic reaction or an exothermic reaction?
(b) What effect would this reaction have on the temperature of its surroundings? Compare the temperature of the surroundings before the reaction takes place to the temperature of the surroundings after the reaction takes place.
(c) What does the equation communicate about the relative energy of the
2. Define and distinguish among the following terms: thermal energy, heat,
and temperature.
3. Use the following information to answer the questions below:
Q = m × c × DT
Q = heat (J)
m = mass (g)
c = specific heat capacity (J/g · °C)
DT = Tf– Ti (°C)
For water, c = 4.184 J/g · °C
(a) A 50.0 g sample of water at 80.0 °C is mixed in a calorimeter with a 50.0 g sample of water at 5.0 °C. What is the final temperature of the water?
(b) A reaction raises the temperature of 100.0 g of water by 3.20 °C. how much heat does the reaction release?
(c) 5 g of iron at 75.0 °C is added to 150.0 g of water at 15.0 °C in a calorimeter. What is the final temperature of the iron and the water? (For iron,
c = 0.444 J/g • °C.)
4. Rubbing alcohol often contains propanol, C 3 H 7 OH(l). Suppose that you have an 85.9 g sample of propanol.
a. How many carbon atoms are in the sample?
b. How many hydrogen atoms are in the sample?
c. How many oxygen atoms are in the sample?
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