Thermo

Front 1

This indicates the direction of energy flow

Back 1

The sign of Δ; E

Front 2

ΔE > 0 means that

Back 2

the energy of the final state of the system is greater than that of the initial state. There is a net flow of energy into the system to increase the system energy.

Front 3

ΔE < 0

Back 3

means that the energy of the final state of the system is less than that of the initial state. There is a net flow of energy out of the system to decrease its energy.

Front 4

ΔE = 0

Back 4

means that the energy of the final and initial states of the system are the same. There can be no net flow of energy.

Front 5

First Law of Thermodynamics

Back 5

ΔE_univ = 0 for all processes

Front 6

The_________in a thermodynamic problem is simply that portion of the universe that is being studied.

Back 6

system

Front 7

A system exchanges energy with iis

Back 7

surroundings

Front 8

The system and its surroundings constitute the

Back 8

thermodynamic universe

Front 9

ΔE_univ equals

Back 9

ΔE + ΔE_surroundings

Front 10

We conclude that the first law of thermodynamics implies that the energy of a system can be changed only by

Back 10

exchanging energy with its surroundings

Front 11

q > 0

Back 11

The system absorbs heat, which increases its energy

Front 12

Processes in which heat enters the system are said to be

Back 12

endothermic

Front 13

q < 0

Back 13

The system gives off heat, which lowers its energy

Front 14

Processes in which heat leaves (exits) the system are said to be

Back 14

exothermic

Front 15

w > 0

Back 15

Work is done on the system, so the energy of the system increases

Front 16

Work is done by the system, so the energy of the system decreases.

Back 16

w < 0

Front 17

the two most common ways to move energy between a system and its surroundings

Back 17

Heat (q) and work (w)

Front 18

ΔE =

Back 18

q + w

Front 19

The enthalpy of reaction

Back 19

is the heat absorbed at constant T and P. It is positive for endothermic reactions and negative for exothermic reactions

Front 20

ΔH

Back 20

(enthalpy) ~ the heat absorbed, so it is positive if the reaction absorbs heat from the surroundings and negative if the reaction gives off heat to the surroundings

Front 21

The reaction is _________ because it gives off heat to the surroundings causing the surroundings to warm.

Back 21

exothermic

Front 22

The reaction is ___________ because it absorbs heat from the surroundings causing the surroundings to cool.

Back 22

endothermic

Front 23

What happens when the reactants are higher in enthalpy than the products, so energy must be given off to the surroundings when the reactants are converted to products.

Back 23

exothermic reaction

Front 24

What happens when the reactants are lower in enthalpy than the products, so energy must be absorbed from the surroundings to convert the reactants to products

Back 24

endothermic reaction

Front 25

ΔH⁰

Back 25

standard enthalpy of reaction

enthalpy change for a reaction in which all reactants and products are in their standard states

also, the amount of heat given off or absorbed when the specified number of moles of each substance reacts or is produced

Front 26

thermochemical equation

Back 26

a balanced chemical equation that includes a thermodynamic property such as ΔH⁰

Front 27

When the coefficients of a chemical equation are multiplied by some number, what happens?

Back 27

then the enthalpy of the resulting reaction equals the enthalpy of the original reaction multiplied by the same number

Front 28

What happens to the sign of ΔH⁰ when reaction is reversed?

Back 28

Sign changes:

H2O(s) --> H2O(l) ΔH⁰ = +6 kJ
H2O(l) --> H2O(s) ΔH⁰ = -6 kJ

Front 29

combustion

Back 29

is the reaction of a substance with oxygen, and it is the major source of harnessed energy

Front 30

combustion reactions always:

Back 30

give off energy

exothermic

(-ΔH⁰)

Front 31

enthalpy of combustion

Back 31

the heat absorbed when one mole of the substance reacts with O2 at standard conditions

Front 32

bond energy or dissociation energy (D)

Back 32

the energy required to break one mole of bonds in the gas phase

Front 33

enthalpy of a reaction

Back 33

can be approximated by the sum of the bond energies of the bonds that must be broken less the sum of the bond energies of those that must be formed

ΔH ~ Σ Dbroken - Σ Dformed