Thermochemistry

Study of chemical reactions and the energy changes involving heat.

Potential Energy

energy an object possesses by virtue of its position or chemical composition

First Law of Thermodynamics

Energy can be converted from one form to another, but it is neither created nor destroyed.

Energy is released when bonds are

Formed

Energy is consumed when bonds are

Broken

Open System


can exchange heat and mass with its surroundings.

Closed System


can only exchange heat with the surroundings (not mass).

Isolated System


cannot exchange heat or mass with the surroundings.

The “system” refers to the

chemicals

The “surroundings” refer to

everything else (aka NOT chemicals)

What kind of system is this? 

Closed

In this photo, hydrogen and oxygen is

the system

In this photo the cylinder is

The surroundings

What is Internal Energy (E)?

sum of all kinetic and potential changes of the system.

We generally don’t know (E), we only know…

how it changes

In a chemical reaction, the initial state of the system (E initial)

refers to the reactants.

In a chemical reaction, the final state of the system (E final)

refers to the products

In this example

H₂ (g)+ O₂ (g) —> 2H₂O (l)

The system will…

Lose energy because bonds are beings formed.

Exergonic

When the system releases energy from the surroundings.

Exergonic will give a ______ value

negative

As a system undergoes a change,

its internal energy can change, and energy can be transferred

When the system gains heat, q will have a _____ value.

positive

When the system loses heat, q will have a ______ value.

negative

When the work is done by the system on the surroundings

(w) will have negative values.

When the work is done on the system by the surroundings (w)

will have positive values.

Endergonic

When a system absorbs energy from the surroundings.

Endothermic

Heat is absorbed by the system from the surroundings

Exothermic

Heat is released by the system into the surroundings.

Because internal energy (E) is a state function,

it depends on the current state of matter, but not how it got to that state of matter.

Enthalpy

The internal energy plus the product of pressure and volume

The value of enthalpy cannot be measured but..

the change of enthalpy can

When a process takes place in constant pressure, and only volume and pressure do work

then we can account for heat flow by measuring the enthalpy of the system.

Enthalpy of reaction ΔH

The change in enthalpy, or also known as change in heat

The process is endothermic when the ΔH value

is positive

The process is exothermic when the ΔH value

is negative

Enthalpy is an _____ property, meaning it _______ on mas

extensive; depends

Enthalpy is a _____ function.

state

The enthalpy change for a reaction is _____ in magnitude, but ______ in sign.

equal; opposite

What is Internal Energy (E)?

sum of all kinetic and potential changes of the system.

Enthalpy is useful for

discussing heat flow in processes that occur under constant pressure.

state function (or state variable)

depends on the current state of matter, however it does not care how it got to that state.