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Ch.5 - Thermochemistry
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Non è quello che usi tu?Cambia libro di testo
Capitolo 5, Problema 55a

When a 6.50-g sample of solid sodium hydroxide dissolves in 100.0 g of water in a coffee-cup calorimeter (Figure 5.18), the temperature rises from 21.6 to 37.8 °C (a) Calculate the quantity of heat (in kJ) released in the reaction.

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1
Identify the mass of the solution, which is the sum of the mass of sodium hydroxide and the mass of water.
Use the specific heat capacity of water (4.18 J/g°C) to calculate the heat absorbed by the solution using the formula: q = m * c * ΔT, where m is the mass of the solution, c is the specific heat capacity, and ΔT is the change in temperature.
Calculate the change in temperature (ΔT) by subtracting the initial temperature from the final temperature.
Convert the calculated heat from joules to kilojoules by dividing by 1000.
Since the heat is released by the reaction, express the final answer as a negative value to indicate exothermic reaction.

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Heat Transfer and Calorimetry

Calorimetry is the science of measuring the heat of chemical reactions or physical changes. In this context, the heat released when sodium hydroxide dissolves in water can be calculated using the formula q = mcΔT, where q is the heat absorbed or released, m is the mass of the solution, c is the specific heat capacity of water, and ΔT is the change in temperature.
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Constant-Pressure Calorimetry

Specific Heat Capacity

Specific heat capacity is the amount of heat required to raise the temperature of one gram of a substance by one degree Celsius. For water, this value is approximately 4.18 J/g°C. Understanding this concept is crucial for calculating the heat change in the calorimeter when the sodium hydroxide dissolves and the temperature of the water increases.
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Dissolution and Exothermic Reactions

The dissolution of sodium hydroxide in water is an exothermic process, meaning it releases heat. This release of heat causes the temperature of the solution to rise, which is a key observation in calorimetry experiments. Recognizing that the dissolution process is exothermic helps in understanding the overall energy changes involved in the reaction.
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Endothermic & Exothermic Reactions