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Chemistry- Structure & Bonding > Enthalpy > Flashcards

Enthalpy Flashcards

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1
Q

Definition of enthalpy

A

The heat content stored in a chemical system

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2
Q

Exothermic reaction

A

A reaction in which heat is lost to its surroundings

The enthalpy of the products is lower than the reactants made

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3
Q

Endothermic reaction

A

A reaction in which heat s taken in from the surroundings

The enthalpy of the products are higher than the enthalpy of the reactants

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4
Q

How does a self heating can work using calcium oxide and water

A

The calcium oxide and water are separated by a barrier
Pull a ring you separate barrier, the 2 compounds REACT
releasing heat

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5
Q

Examples of exothermic reactions

A

Oxidation/ combustion

RESPIRATION

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6
Q

eXAMPLES OF endothermic reaction

A

photosynthesis

thermal decompositon

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7
Q

Definition of an enthalpy profile diagram

A

Diagram for a reaction to compare the enthalpy of the REACTANTS with the enthalpy OF THE PRODUCTS

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8
Q

x AND Y AXIS OF ENTHALPY PROFILE DIAGRAM

A

X- progression of reaction

Y- enthalpy

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9
Q

Activation energy

A

Minimum energy required to start a reaction by BREAKING BONDS

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10
Q

wHAT are standard condition

A

1 Atm
250c
1 molddm-3

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11
Q

wHAT IS MEANT BY STANDARD STATES

A

The physical state of a substance under STANDARD CONDITIONS

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12
Q

Definition of the standard enthalpy change of reaction

A

The enthalpy change that takes accompanies a reaction when molar quantities of reactants of products as expressed in the equation react under stanadard conditions all being in their standard states

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13
Q

Standard enthalpy of combustion

A

The enthalpy change that takes place when one mole of a FUEL is burned COMPLETELY in oxygen under standard condition, all products and reactants being in their standard states

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14
Q

Standard enthalpy change of formation

A

The enthalpy change that takes places when ONE MOLE of a compound is formed from its constituent elements in their standard states, under standard conditions

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15
Q

Specific heat capacity

A

The energy required to raise the temperature of of 1g of a substance by 1 degree c

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16
Q

An experiment to measure SHC

A

Calorimetry

17
Q

Process of finding enthalpy change using Q=Mdelta T

A

Find Q by subbing
find amount in moles that was reacted
Divide by 1 to work out KJ/mol

18
Q

Two theoretical methods of calculating enthalpy

A

Mean bond dissociation

Enthalpy cyccle

19
Q

Describe the experimental method to determine the enthalpy change of combustion for a fuel

A

Burn a known mass of a substance in air
Heat up a n=know mass of water
measure temperature change in water

20
Q

WHy is there a difference between the the experimental value and the standard value

A

Incomplete combustion

Heat may be lost to surroundings

21
Q

To get a better agreement of an experiemental enthalpy change what can you do

A

Cut down on heat loss

Ensure complete combustion

22
Q

How is a bomb calorimeter a better way of measuring

A

Ensures fuel burns in complete combustion

Heat is transferred to water…welll insulated… reduces heat loss to surroundings

23
Q

;Bond enthalpy defintion

A

The enthalpy change that takes place when breakind by HOMOLYTIC FISSION 1 mol of a given bond in the molecules of a GASEOUS SPECIES

24
Q

Average bond enthalpy

A

The avverage enthalpy change that takes place when one mole of a given bond is broken by HOMOLYTIC FISSION
IN THE MOLECULES OF A GASEOUS SPECIES

25
Q

When is bond enthalpies endo and exothermic

A

Endothermic when bonds are BROKEN
Exothermic when bonds are MADE
MEXICAN BENDER

26
Q

EQUATION TO MEASURE DELTA H USING BOND ENTHALPIES

A

BOnds broken- bonds made

27
Q

Hess’s law

A

If a reaction takes place by more than one route and the
intiial and final conditions are the same
the total energy change is the same for each route

28
Q

Enthalpy cycle defintion

A

Diagram showing alternative routes between reactants and products
allows indirect determination of EC
from other ECs using Hess’s law

Chemistry- Structure & Bonding (9 decks)

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