9.1 The Nature of Energy

What is the symbol for internal energy?

E

What is energy?

the capacity to do work or produce heat

What is the symbol for Internal Energy?

E

Is energy a state function?

Yes, it is independent of the pathway

What is energy the sum of?

the kinetic and potential energy of all particles in the system

How can energy be changed?

by a flow of work, heat, or both

Equation for Internal Energy

∆E = q + w

What does ∆E mean?

change in the system’s internal energy

what does q mean?

heat

what does w mean?

work

For the equation, ∆E = q + w, what is special about the units of q and w?

units have to be the same, usually are joules

What does a negative or positive sign indicate?

the direction of flow from the system’s point of view

Endothermic reaction flow of q

energy (heat) flows into the system, so q (heat) is positive

Exothermic reaction flow of q

energy (heat) flows out of the system, so q (heat) is negative

If the surroundings do work on the system, w is?

energy flows into the system, so w (work) is positive

If the system does work on the surroundings, w is?

energy flows out of the system, so w (work) is negative?

law of conservation of energy

energy can be converted from one form to another but never destroyed

What is the change in energy of the universe?

0, energy of the universe if constant

what is potential energy?

energy due to position or composition

• attractive and repulsive forces

The energy released when gasoline is burned (combustion) results from…

the difference in attractive forces between nuclei and electrons in the reactants and products

• potential energy

kinetic energy

due to the motion of an object, depends on mass and volume

• KE = 1/2mv²

As a ball rolls down a hill, some of it’s kinetic energy is transferred…

to the surface of the hill as heat aka frictional heating

• temperature of the hill increases very slightly

Temperature

a property that reflects the random motions of particles in a particular substance

Is temperature a state function?

yes it is a state function, independent of the pathway

Heat (q)

ability to change temperature

• involves the transfer of energy between two objects due to a temperature difference

Is heat a substance contained in an object?

no

Symbol for heat and is it a state function

q and not a state function, dependent on the pathway

What is work (w)?

a force acting over a distance

• how energy can be transferred

symbol for Work and is Work a state function?

w and not a state function, dependent on the pathway

Equation for work

w = P_ext∆V

Equation for Work in an expanding gas

Volume increases, so work is negative and work flows out of the system

• w = -P_ext∆V

Equation for Work in an compressed gas

Volume decreases, so work is positive and work flows into the system

• w = P_ext∆V

external pressure

pressure that causes a compression or that resists an expansion

Two ways to transfer energy…

through work and heat

state function/property

a property of a system that depends only on its present state

• foes not depend on how the system arrived at the present state

system

part of the universe we focus attention on

surroundings

includes everything else in the universe