Glossary
Bomb Calorimeter
A device used to measure the heat of combustion reactions at constant volume, typically by igniting a sample in a sealed container surrounded by water.
Example:
Food scientists use a bomb calorimeter to precisely determine the caloric content of snacks by burning them and measuring the heat released.
Calorimetry
The scientific process of measuring the heat flow into or out of a substance or system.
Example:
A chemist uses calorimetry to determine the energy content of a new biofuel by burning it in a controlled environment.
Change in Temperature (ΔT)
The difference between the final and initial temperatures of a substance, indicating the extent of heating or cooling.
Example:
A large ΔT for a substance indicates a significant amount of heat was either absorbed or released.
Coffee-Cup Calorimeter
A simple, insulated device, often made from styrofoam cups, used to measure heat changes in reactions occurring in aqueous solutions at constant pressure.
Example:
In a high school lab, students often use a coffee-cup calorimeter to determine the specific heat of a metal by mixing it with water.
Constant-Pressure Calorimeter
A device designed to measure heat changes for reactions occurring at constant atmospheric pressure, where the heat transferred is equivalent to the change in enthalpy (ΔH).
Example:
Dissolving a salt in water in a simple coffee cup setup is an example of an experiment conducted using a constant-pressure calorimeter.
Endothermic
A process or reaction that absorbs heat from its surroundings, resulting in a decrease in the temperature of the surroundings and a positive ΔH.
Example:
An instant cold pack feels chilly because the chemical reaction inside is endothermic, drawing heat from your skin.
Enthalpy (H)
A thermodynamic property representing the total heat content of a system at constant pressure. It cannot be measured directly.
Example:
While we can't measure the absolute enthalpy of a cup of coffee, we can measure the change in its enthalpy as it cools.
Exothermic
A process or reaction that releases heat to its surroundings, resulting in an increase in the temperature of the surroundings and a negative ΔH.
Example:
The burning of wood is an exothermic reaction, releasing heat and light into the environment.
First Law of Thermodynamics
A fundamental principle stating that energy cannot be created or destroyed, only transferred or converted from one form to another.
Example:
When a battery powers a flashlight, the chemical energy is converted to light and heat energy, illustrating the First Law of Thermodynamics.
Heat (q)
The transfer of thermal energy between objects or systems due to a temperature difference.
Example:
When you touch a hot stove, the heat transfers from the stove to your hand, causing a burn.
Heat Loss = Heat Gain
A principle derived from the First Law of Thermodynamics, stating that in an isolated system, the heat lost by one component equals the heat gained by another.
Example:
When a hot metal is placed in cool water, the heat loss = heat gain principle allows us to calculate the specific heat of the metal.
Mass (m)
A measure of the amount of matter in an object, typically expressed in grams or kilograms in calorimetry calculations.
Example:
In a calorimetry experiment, accurately measuring the mass of the water is crucial for calculating the heat absorbed.
Specific Heat (C)
The amount of heat energy required to raise the temperature of one gram of a substance by one degree Celsius (or Kelvin).
Example:
Water has a high specific heat, which is why coastal areas experience milder temperature fluctuations compared to inland regions.
q = mCΔT
The fundamental equation used to calculate the amount of heat (q) transferred, where m is mass, C is specific heat, and ΔT is the change in temperature.
Example:
To find out how much heat is needed to warm a swimming pool, you would use the q = mCΔT equation, plugging in the water's mass, specific heat, and desired temperature change.
ΔH (Change in Enthalpy)
The change in heat content of a system at constant pressure, representing the heat absorbed or released during a chemical reaction or physical process.
Example:
The ΔH for the combustion of methane is negative, indicating that the reaction releases heat to the surroundings.