Chapter 06: Thermochemistry Flashcards Preview

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Flashcards in Chapter 06: Thermochemistry Deck (35):
1

Energy

The capacity of matter to do work

2

Work

w

w = F×d
(work = force × distance)

The action of a force through a distance.

3

Heat

q

The flow of energy caused by a difference in temperature

4

Types of energy (4)

Kinetic energy (due to motion)

Thermal energy (associated with temperature)

 

Potential energy (due to position/composition)

Chemical energy (associated with positions of electrons and nuclei)

5

Heat v. Temperature

Transfer of thermal energy v. measure of thermal energy

6

Thermal equilibrium

Heat flows from matter with high temperature to matter with low temperature until both objects reach the same temperature.

7

Thermochemistry

Study of relationships between chemistry and energy

8

System

Specific part of the universe that is of interest in a study

9

Surroundings

Everything else with which the system can exchange energy

10

Open system

Mass & energy is exchanged

11

Closed system

ONLY energy is exchanged (not mass)

12

Isolated system

Neither mass nor energy is exchanged (no exchange at all)

13

Kinetic energy

KE = 1/2mv2
(half of mass × velocity squared)

Directly portional to m and v

Units: kg×m2/s2

14

1 J = ? KE

1 J = 1 kg×m2/s2

15

1 cal = ? J

1 cal = 4.184 J

16

1 Cal = ? cal

1 Cal = 1000 cal (or 1 kcal)

17

Exothermic reaction

Releases heat by transferring thermal energy from system to surroundings

18

Endothermic reaction

System gains heat from surroundings to react

19

Internal energy

E

Sum of KE + PE of all particles within a system

20

Change in internal energy

ΔE = Eproducts - Ereactants

21

State function

Function that depends only on intial and final conditions

22

First law of thermodynamics

Energy can be converted from one form to another, but it cannot be created nor destroyed

Total energy of universe is contant

Thus:

ΔEsystem = -ΔEsurroundings

and:

ΔE = q + w

*q (heat) is positive when energy is gained
negative when energy is lost

*w is positive when work is done ON the system
negative when work is done BY the system

23

Energy exchange

Accomplished through heat and work between system and surroundings

24

Pressure-volume work

Occurs when the force is caused by a volume change against an external pressure

w = -PΔV

work = the negative of external pressure × change in volume

work done = -w!

25

1 L×atm = ? J

1 L×atm = 101.3 J

26

Enthalpy

H

H = E + PV
(internal energy + pressure×volume)

*State function

27

Enthalpy change

ΔH

The heat (q) evolved in a reaction at constant pressure

ΔH = qp

ΔH = Hproducts - Hreactants

28

Heat capacity

C

q = C × Δt

The amount of heat (q) required to raise the temperature of a given quantity (m) of a substance by 1°C

Units: J/°C or J/K

Proportionality constant

System absorbs heat = tempature increase
Directly proportional

29

Specific heat capacity

Cs
units: J/g × °C

A measure of a substance's instrinsic ability to absorb heat

The amount of heat (q) required to raise the temperature of 1 gram of a substance by 1 °C

q = m × Cs × Δt

30

Molar heat capacity

The amount of heat (q) required to raise the temperature of 1 mole of a substance by 1°C

Units: J/mol °C

31

Bomb calorimeter

Constant-volume calorimetry

Since volume is constant, no work is done, w = 0

Thus:

ΔErxn = qv = qrxn

-qrxn = qcal = Ccal × ΔT

qcal is heat absorbed by calorimeter
-qrxn is heat released by reaction
Ccal is heat capacity of calorimeter

32

Coffee-cup calorimetry

Constant-pressure calorimetry

Used to measure enthalpy of a reaction: ΔHrxn

qsoln = msoln × Cs, soln × ΔT

and

qrxn = -qsoln = qp =  ΔHrxn

33

Standard enthalpy of formation

ΔHf°

The heat change that results when one mole of a compound is formed from its elements at a pressure of 1 atm

ΔHf° of any element in most stable form is zero

stable liquids: Hg, Br

stable gases: H2, N2, O2, F2, Cl2, noble gases

note: C graphite is stable, not C diamond, though

note: S8 rhombic is stable

34

Standard enthalpy of a reaction

ΔHrxn°

The enthalpy of a reaction carried out at 1 atm

ΔHrxn° = ΣnproductsΔHf° - ΣnreactantsΔHf°

n = number of moles

35

Hess' law

When reactants are converted to products, the change in enthalpy is the same whether the reaction takes place in one step or a series of steps

ΔHrxn° = ΔH1° + ΔH2°