BackMatter and Energy: Specific Heat and Its Applications
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Matter and Energy
Introduction to Specific Heat
Specific heat is a fundamental concept in chemistry that describes how substances absorb and release heat. Understanding specific heat is essential for explaining temperature changes in different materials and for solving problems related to heat transfer in chemical and biological systems.
Specific heat (SH) is the amount of heat required to raise the temperature of exactly 1 gram of a substance by exactly 1°C.
Specific heat values are different for different substances, reflecting their unique molecular structures and bonding.
Units: Joules per gram per degree Celsius (J/g°C) in the SI system, and calories per gram per degree Celsius (cal/g°C) in the metric system.
Example: Water has a high specific heat, which helps moderate temperatures in environments near large bodies of water.
Formula for Specific Heat
The specific heat of a substance can be calculated using the following relationship:
Formula:
Where SH is specific heat, heat is the energy absorbed or released (in J or cal), mass is in grams, and ΔT is the temperature change in °C.
For water:
Calculating Specific Heat: Example Problem
To determine the specific heat of a substance, you can use experimental data involving mass, heat absorbed, and temperature change.
Example: What is the specific heat if 24.8 g of a metal absorbs 275 J of energy and the temperature rises from 20.2°C to 24.5°C?
Step 1: State the given and needed quantities.
Given: mass = 24.8 g, heat = 275 J, = 20.2°C, = 24.5°C
Need: Specific heat (SH)
Step 2: Calculate the temperature change ():
Step 3: Write the relationship for specific heat:
Step 4: Substitute the values and solve:
Specific Heats for Some Substances
Different substances have characteristic specific heat values. Metals generally have lower specific heats than water, meaning they heat up and cool down more quickly.
Substance | cal/g°C | J/g°C |
|---|---|---|
Aluminum, Al(s) | 0.214 | 0.897 |
Copper, Cu(s) | 0.0920 | 0.385 |
Gold, Au(s) | 0.0308 | 0.129 |
Iron, Fe(s) | 0.108 | 0.452 |
Silver, Ag(s) | 0.0562 | 0.235 |
Titanium, Ti(s) | 0.125 | 0.523 |
Applications and Implications of Specific Heat
Water's high specific heat helps regulate climate by absorbing and releasing large amounts of heat with little temperature change.
Metals with low specific heat are used in applications where rapid temperature changes are needed (e.g., cooking utensils).
Desert sand, with low specific heat, heats up quickly during the day and cools rapidly at night.
Calculations Using the Heat Equation
When the specific heat of a substance is known, you can calculate the heat lost or gained by a given mass over a certain temperature change using the heat equation:
Example: Calculate the energy needed to heat 255 g of copper from 24°C to 185°C.
Step 1: Given: mass = 255 g, = 24°C, = 185°C, J/g°C
Step 2: Calculate :
Step 3: Use the heat equation:
(rounded to three significant figures)
Conceptual Questions and Answers
When ocean water cools, the surrounding air: Warms (because the water releases heat to the air).
Sand in the desert is hot in the day and cool at night. Sand must have a: Low specific heat (it changes temperature quickly).
