Enthalpy Flashcards

1
Q

Can enthalpy be measure directly?

A

No

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2
Q

Enthalpy change symbol

A

🔼H

Delta H

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3
Q

Enthaply change definition

A

The enthalpy change of a reaction is the heat energy change with its surroundings at constant pressure.

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4
Q

Enthalpy change units

A

kj mol^(-1)

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5
Q

Delta meaning

A

Change

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6
Q

Standard enthalpy changes are measured at…?

A
Standard pressure (100 kPa)
Standard temperature (298 K)

Symbol ΔHθ. But θ is superscript

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7
Q

-ΔΗ is it exothermic or endothermic?

A

Exothermic

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8
Q

+ΔΗ is it exothermic or endothermic?

A

Endothermic

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9
Q

GRAPHS

A

SEE PAPER

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10
Q

Standard enthalpy of reaction symbol

A

θ
ΔΗ
R

The r for reaction is replaced by a specific letter for particular standard enthalpies

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11
Q

Standard enthalpy of Formation symbol

A

θ
ΔΗ
f

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12
Q

Standard enthalpy of formation definition

A

This is the enthalpy change when 1 MOLE of a substance is FORMED from its ELEMENTS under standard conditions (100kPa and 298k) with all substances in their standard STATES (eg. Solid, liquid gas)

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13
Q

Standard enthalpy of formation value of an element in its standard state

A

Must be 0

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14
Q

Standard enthalpy of formation equation for H2O

A

H2 + 1/2 O2 ➡️ H2O

To form one mole of water

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15
Q

Standard enthalpy of combustion symbol

A

θ
ΔΗ
c

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16
Q

Standard enthalpy of combustion definition

A

This is the enthalpy change when 1 MOLE of a substance undergoes COMPLETE COMBUSTION under standard conditions (100kPa and 298K) with all substances being in their standard states

17
Q

What is meant by the term ‘standard states’ of a substance

A

Normal state at room temperature eg. Solid, liquid or gas

18
Q

What are standard conditions

A

100kPa (kilo pascals)

298K (kelvin)

19
Q

Standard enthalpy of combustion equation for CH4

A

CH4 + 2O2 ➡️ CO2 + 2H2O

20
Q

Standard enthalpy of atomization symbol

A

θ
ΔΗ
a

21
Q

Standard enthalpy of atomization definition

A

This is the enthaply change when 1 MOLE of GASEOUS ATOMS of a substance are FORMED from the substance in its standard state under standard conditions (100kPa and 298K)

22
Q

Standard enthalpy of atomization equation for chlorine

A

1/2 Cl2 (g) ➡️ Cl (g)

Cl2 is how is appears normally then Cl is the one mole that is formed

23
Q

Standard enthalpy of neutralization symbol

A

θ
ΔΗ
n

24
Q

Standard Enthalpy of neutralization definition

A

This is the Standard Enthalpy change when 1 MOLE of WATER is produced by the reaction of an ACID and a BASE under standard conditions (100kPa and 298K) with all substances being in their standard states

25
Q

Standard Enthalpy of neutralization equation for sulphuric acid and sodium hydroxide

A

BALANCED EQUATION. H2SO4 + 2NaOH ➡️ Na2SO4 + 2H2O
(Wrong as 2 moles of water)

Answer: 1/2 H2SO4 + NaOH ➡️ 1/2 Na2SO4 + H2O

26
Q

In an exotherimic reaction does it give out energy to its surroundings or take energy in? And does the temperature of the reaction decrease or increase?

A

Gives OUT energy to surroundings

Reaction temperature gies UP
so -ΔΗ as the products of the reaction end up with LESS energy than the reactants

27
Q

In an endothermic reaction does it give out energy to its surroundings or take energy in? And does the temperature of the reaction decrease or increase?

A

Takes IN energy from surroundings

Reaction temperature DEACREASES

Products have MORE energy than the reactants so ΔΗ is a positive value as

28
Q

Give the notation for an enthaply change under standard conditions at a temperature of 298K

A

θ
ΔΗ
298

29
Q

Describe the difference between endothermic and exothermic reactions

A

Exothermic gives OUT heat

Endothermic takes IN heat

30
Q

Enthalpy definition

A

The enthalphy of a system is a measure of the energy stored in (or heat content) of a system. Symbol H