Chemistry: Chapter 15

A balanced chemical equation including the physical states of all reactants and the energy change.

How are thermochemical equations for chemical reactions and other processes written?

Chemical potential energy is the source of energy in a substance. During an exothermic reaction, bonds break and form and protons go from an area of higher potential energy to lower potential energy.

How can chemical potential energy be related to the heat gained or lost in chemical reactions?

Potential energy is the stored energy in any object or system by virtue of its position or arrangement of parts. Kinetic energy is the energy if an object or a system's particles in motion.

How do potential and kinetic energy differ?

A known mass of water is placed in an insulated contained to absorb the energy released from the reacting system or to provide the energy absorbed by the system. The data to be collected is the change in temperature of this mass of water.

How is a calorimeter used to measure energy that is absorbed or released?

When matter changes from a liquid to a solid, it loses energy. When matter changes from a solid to a liquid, it absorbs energy from its surroundings. For example, you shiver after stepping out of a hot shower because your skin provides the heat needed to vaporize the water.

How is energy lost or gained during changes of state?

By using the equation, q = c x m x ΔT

How is heat that is absorbed or released in a chemical reaction calculated?

q = c x m x ΔT (q = heat energy transferred, m = mass of the liquid being heated, c = specific heat capacity of the liquid, deltaT = change in temperature of the liquid)

How is the amount of heat absorbed or released by a substance calculated as its temperature changes?

System

In thermochemistry, the specific part of the universe containing the reaction or process being studied

Joule

SI unit of heat and energy

Energy

The capacity to do work or produce heat; exists as potential energy, which is stored in an object due to its composition or position, and kinetic energy, which is the energy of motion.

enthalpy (heat) of reaction

The change in enthalpy for a reaction - the difference between the enthalpy of the substances that exist at the end of the reaction and the enthalpy of the substances present at the start.

Enthalpy

The heat content of a system at constant pressure

Second law of thermodynamics

The spontaneous processes always proceed in such a way that the entropy of the universe increases

Enthalpy is the heat content of a system at constant pressure. The change in Enthalpy is the heat absorbed or released by the reaction.

What do Enthalpy and Enthalpy change mean in terms of chemical reactions?

The capacity to do work or produce heat

What is energy?

Thermochemical equation

a balanced chemical equation that includes the physical states of all reactants and products and the energy change, usually expressed as the change in enthalpy.

Heat

a form of energy that flows from a warmer object to a cooler object

Entropy

a measure of the number of possible ways that the energy of a system can be distributed; related to the freedom of the system's particles to move and the number of ways they can be arranged

Spontaneous process

a physical or chemical change that occurs without outside intervention and may require energy to be supplied to begin the process

Calorimeter

an insulated device that is used to measure the amount of heat released or absorbed during a physical or chemical process

Surroundings

in thermochemistry, includes everything in the universe except the system

Universe

in thermochemistry, is the system plus the surroundings

Hess's Law

states that if two or more thermochemical equations can be added to produce a final equation for a reaction, then the sum of the enthalpy changes for the individual reactions is the enthalpy change for the final reaction

Law of Conservation of Energy

states that in any chemical reaction or physical process, energy may change from one form to another, but it is neither created nor destroyed

Molar Enthalpy (heat) of fusion

the amount of heat required to melt one mole of a solid substance

Specific heat

the amount of heat required to raise the temperature of one gram of a given substance by one degree Celsius

Calorie

the amount of heat required to raise the temperature of one gram of pure water by one degree Celsius

Molar Enthalpy (heat) of vaporization

the amount of heat required to vaporize one mole of a liquid

Standard Enthalpy (heat) of formation

the change in enthalpy that accompanies the formation of one mole of a compound in its standard state from its constituent elements in their standard states

Free energy

the energy available to do work--the difference between the change in enthalpy and the product of the entropy change and the kelvin temperature

Chemical potential energy

the energy stored in a substance because of its composition; most is released or absorbed as heat during chemical reactions or processes

molar enthalpy (heat) of combustion

the enthalpy change for the complete burning of one mole of the substance

Thermochemistry

the study of heat changes that accompany chemical reactions and phase changes