Thermochemistry

Introduction

In this module, you will study thermochemistry. Thermochemistry is the study of the heat released by, or absorbed from, chemical reactions. It is a branch of thermodynamics and is utilized by a wide range of scientists and engineers.

Having a periodic table handy is always helpful in chemistry. You may always use a periodic table on assignments, quizzes, and tests in this course.

Download the periodic table.

Module Lessons Preview

In this module, we will study the following topics:

The Law of Thermodynamics

Heat and Calorimetry

Calorimetry Lab

Key Terms

kinetic energy - The energy possessed by a body because of its motion, equal to one half the mass of the body times the square of its speed.

potential energy - The energy of a particle or system of particles derived from position, or condition, rather than motion. A raised weight, coiled spring, or charged battery has potential energy.

heat - A form of energy associated with the motion of atoms or molecules and capable of being transmitted through solid and fluid media by conduction, through fluid media by convection, and through empty space by radiation.

temperature - A measure of the average kinetic energy of the particles in a sample of matter, expressed in terms of units or degrees designated on a standard scale.

system - Any set of interrelated parts. An open system allows mass and energy to circulate into and out of it; a closed system gives and receives energy but not mass.

surroundings - Everything outside the thermodynamic system.

specific heat capacity - Quantity of heat required to increase temperature of a body by one degree Celsius.

phase diagram - A graph showing the pressures at which phase transitions between different states of a pure compound occur, as a function of temperature.

heat of vaporization - The amount of heat required to convert a unit mass of a liquid at its boiling point into vapor without an increase in temperature.

endothermic - Characterized by or causing the absorption of heat.

exothermic - Denoting a chemical reaction that releases heat into its surroundings.

activated complex - An energetically excited state which is intermediate between reactants and products in a chemical reaction. Also known as the transition state.

activation energy - The energy, in excess over the ground state, which must be added to an atomic or molecular system to allow a chemical process to take place.

heating curve - A heating curve is a graph showing how a substance's phases (gas, liquid or solid) change while being heated.

absolute zero - The theoretical temperature at which substances possess no thermal energy, equal to −273.15°C or −459.67°F or 0 K.

Joule - The SI unit of energy; 1 J = 1 kg m2 s-2.

Calorie (cal) - 4.184 J. The energy that will raise the temperature of 1.00 g of water 1 °C

Thermodynamics - The study of the laws that govern the energy and entropy changes of physical and chemical events

Calorimeter - An apparatus used in the determination of the heat of a reaction

Molar heat of fusion - the heat absorbed when 1 mol of a solid melts to give 1 mol of the liquid at constant temperature and pressure

Molar heat of vaporization - the heat absorbed when 1 mol of a liquid changes to 1 mol of its vapor at constant temperature and pressure

Enthalpy, H - The heat content of a system

Enthalpy change, ΔH - The difference in enthalpy between the initial state and the final state for some change

Hess's law - For any reaction that can be written in steps, the standard heat of reaction is the same as the sum of the standard heats of reaction for the steps

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