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A-level Chemistry > Chapter 9 Enthalpy > Flashcards

Chapter 9 Enthalpy Flashcards

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1
Q

what is enthalpy

A

measure of heat energy in a chemical

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2
Q

what is the symbol for enthalpy

A

H

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3
Q

what is enthalpy change

A

the difference in enthalpies between the products and reactants

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4
Q

what is the enthalpy change formula

A

ΔH = H(products) - H(reactants)

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5
Q

what is conservation of energy

A

fundemental law of science that states that energy cannot be created or destroyed

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6
Q

what is EXOTHERMIC

A

transfer of energy from the system to the surroundings

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7
Q

what is ENDOTHERMIC

A

transfer of energy from the surroundings to the system

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8
Q

what does an enthalpy profile diagram show

A

the relative enthalpies of the reactants and products and the enthalpy change

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9
Q

how does the enthalpy diagram show if a reaction is endothermic or exothermic

A

exothermic reactions have a negative enthalpy change

endothermic reactions have a positive enthalpy change

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10
Q

what is activation energy

A

the minimum amount of energy that must be supplied to the system before the reaction can take place

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11
Q

define standard conditions

A

conditions under which most experiments are and most closely resemble typical working conditions of temperature and pressure

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12
Q

how are standard physical conditions represented

A

⦵ in the superscript

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13
Q

what is the standard pressure value

A

100kPa

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14
Q

what is the standard temperature value

A

298K

25C

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15
Q

what is the standard concentration value

A

1moldm^-3

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16
Q

what is the standard state

A

the normal physical state of a substance under standard temperature and pressure

17
Q

what is the standard enthalpy change of reaction

A

the enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions

18
Q

what is the symbol for standard enthalpy change of reaction

A

ΔrH⦵

19
Q

what is the standard enthalpy change of formation

A

the enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions

20
Q

what is the symbol for standard enthalpy change of formation

A

ΔfH⦵

21
Q

what is standard enthalpy change of combustion

A

the enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions

22
Q

what is the symbol for standard enthalpy change of combustion

A

ΔcH⦵

23
Q

what is standard enthalpy change of neutralisation

A

energy change that accompanies the reaction of an acid by a base to form one mole of H2O(l) under standard conditions

24
Q

what is the symbol for standard enthalpy change of neutralisation

A

ΔneutH⦵

25
Q

what three quantities are required to work out energy change

A

mass
specific heat capacity
temperature change

26
Q

how is mass calculated

A

it is the mass of the water in the aqueous solutions so you take the volume and times it by the density; 1g/cm

27
Q

what is the specific heat capacity value

A

4.18

28
Q

what is the heat energy equation

A 
q = m x c x ΔT
energy = mass x specific heat capacity x temperature change
29
Q

what are the three steps to calculate ΔcH

A

> calculate the energy change
calculate the amount in moles of substance burned
do q/n to find ΔcH

30
Q

what are the four reasons why ΔcH may be different from the theoretical or expected

A

> heat loss to surroundings
incomplete combustion
evaporation of substance
non-standard conditions

31
Q

what are the three steps to calculate ΔrH

A

> calculate the energy change , q
calculate the amount of moles of the reactant that is not in excess
do q/n to find ΔrH

32
Q

what are the three steps to calculate ΔneutH

A

> calculate the energy change , q
calculate the amount in moles of the base + acid that was reacted
do q/n to find ΔneutH

33
Q

what is average bond enthalpy

A

the energy required to break one mole of a specified type of bond in a gaseous molecule

34
Q

why does average bond enthalpy have limitations

A

the actual bond enthalpy can vary depending upon the chemical environment of the bond

35
Q

which energy is endothermic and which is exothermic

A

energy required to break bonds is endothermic

energy released when bonds break is exothermic

36
Q

what is the enthalpy change of reaction equation

A

ΔrH = Σ(bond enthalpies in products) - Σ(bond enthalpies in reactants)

37
Q

what is Hess’ Law

A

the total enthalpy change for an indirect route is the same as that for the direct route

38
Q

what is the value for all ΔneutH⦵ reactions

A

-57kJmol^-1

A-level Chemistry (19 decks)

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