OEnergy Changes in Chemical and Nuclear Reactions

Thermochemistry

the study of energy changes that accompany physical and chemical changes in matter

Changes that occur in matter can be classified as:

Physical

Chemical

Nuclear

What is Energy?

Energy is the ability to do work

SI units OF ENERGY?

joules (J) - *1 KJ = 1000 J*

Matter stores energy in three main ways:

• Kinetic Energy

Potential Energy:

Nuclear Energy

Kinetic Energy:

the energy of an object due to its motion (translation, rotation, vibration)

Potential Energy:

the energy of a body or system due to its position or composition - found in chemical bonds (released when new bonds form)

Nuclear Energy

(stored in the nucleus as energy needed to hold the nucleus together)

Thermal Energy:

total potential and kinetic energy of a substance - often considered a form of kinetic energy due to its connection to the motion of molecules.

Heat:

The transfer of thermal energy from a warm object to a cooler object

Temperature

the average kinetic energy of the particles in a sample, measured in °C or K

Law of Conservation of Energy (4)

The total energy of the universe is constant

• Energy can neither be created nor destroyed

• Energy can be

transferred from one substance to another

• Can be converted into various forms

(1st Law of Thermodynamics

• The total energy of the universe is constant

Chemical System

a set of reactants and products under study, usually represented by a chemical equation

Surroundings

all matter around the system that is capable of absorbing or releasing thermal energy

Δ𝐸system =−Δ𝐸surrounding

Any change in the system is accompanied by an equal and opposite change in the surroundings

Types of Systems

OPEN SYSTEM

CLOSED SYSTEM

ISOLATED SYSTEM

OPEN SYSTEM

A system where both matter and energy can move in and out (Example: Open mug)

CLOSED SYSTEM

A system where energy can move in and out, but not matter (Example: Coffee cup with lid)

ISOLATED SYSTEM

An ideal system, where neither energy or matter can move in or out (Example: insulated coffee cup with lid)

The total energy of a system is equal to...

the sum of the potential and kinetic energy of all species in the system.

When a reaction occurs,___ is transferred between substances

HEAT

• Heat (q)

is the amount of thermal energy transferred between substances

Exothermic Reactions

releasing thermal energy as heat flows out of the system

Endothermic Reactions

absorbing thermal energy as heat flows into the system

Exothermic Reactions: heat (q) flows from the ______to the ______,

heat (q) flows from the system to the surroundings, usually causing an increase in the temperature of the surroundings

Exothermic: q+ or -

negative-- losing heat from the system

Endothermic: q + or -

positive value (q > 0); i.e. adding heat to the system

Endothermic: heat (q) flows from the ___into the ___,

heat (q) flows from the surroundings into the system, usually causing a decrease in the temperature of the surroundings