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Fires & Explosions > Lecture 3 > Flashcards

Lecture 3 Flashcards

1
Q

Are drop test measurements qualitative or quantitative?

A

Drop test measurements are semi-quantitative with an arbitrary scale of sensitivity

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2
Q

What is entropy related to?

A

Related to the volume of gas we generate

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3
Q

What was the issue with gunpowder in the early days?

A

Gunpowder was a useful explosive in early days but it generated a lot of soot (carbon) as it didn’t have enough oxygen, it was oxygen deficient.

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4
Q

What is a desirable property of an explosive?

A

For it to contain oxygen

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5
Q

What is the equation for power?

A

Power = Q x V

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6
Q

What does Q stand for?

A

Heat of explosion (enthalpy)

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7
Q

What does V stand for?

A

Volume of gas in moles

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8
Q

What do Kistiakowsky rules predict?

A

It predicts the products of an explosion

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9
Q

What does the oxygen balance dictate?

A

Oxygen balance dictates whether a detonation consumes external O2

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10
Q

What determines the oxygen balance?

A

The molecular formula determines the oxygen balance

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11
Q

What is the formula to determine the number of oxygen atoms required?

A

Ω (OB) = ([d - 2a - (b/2)] x 16) / M) x 100
a = Number of Carbon atoms
b = Number of Hydrogen atoms
c = Number of Nitrogen atoms
d = Number of Oxygen atoms

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12
Q

How do you calculate oxygen balance as a mole percentage?

A

Ω = (([d - 2a - b/2] x 16) / molecular weight) x 100

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13
Q

What decimal place should you use for the molecular weight of the explosive in the oxygen balance equation?

A

To the nearest whole number as the calculation is only an approximation

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14
Q

If you have a negative oxygen balance what does this suggest?

A

This suggests the molecule is oxygen deficient

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15
Q

What does an oxygen balance of 0 indicate?

A

This suggests there is exactly enough oxygen to make CO2 and H2O

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16
Q

When are the Kistiakowsky-Wilson rules applied?

A
  • When the oxygen balance is between 0 and -40%
  • Oxygen balance is < -40%
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17
Q

What does it mean if the oxygen balance is less than 0?

A

If the oxygen balance is less than zero the carbon and hydrogen cannot be fully oxidised

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18
Q

What are the K-W rules used to determine?

A

K-W ‘rules’ can be used to determine what the products of detonation actually are

19
Q

If the oxygen balance is higher than -40% what rules should be used?

A

The modified K-W rules

20
Q

What do the K-W rules prioritise?

A

It prioritises the use of limited oxygen atoms to form reaction products

21
Q

Are the K-W rules used for detonation or combustion?

A
  • They are used for detonation
  • Combustion is when you use oxygen from the atmosphere
22
Q

What gaseous product would qualitatively indicate a near-neutral or positive oxygen balance?

A

CO2 would indicate this as it is the last stop in the KW rules and is only formed when we have oxygen left over.

23
Q

How do you calculate the enthalpy of detonation? (Q or ΔdH)

A

Sum of the enthalpy formation of the products - sum of the enthalpy formation of the reactants

24
Q

What is the enthalpy of formation for compounds in a standard state?

A

0

25
Q

What does the volume of detonation depend on?

A

The volume of detonation depends on the moles of gas released

26
Q

Other than the volume of detonation, what is the moles of gas a measure of?

A

The entropy change

27
Q

What is the volume for one mole of gas?

A

22.4 1mol-1 as we treat all gases as ideal gases and assume the occupy about the same volume

28
Q

What is the explosive power a measure of?

A

The explosive power is a measure of both enthalpic and entropic components of an explosion

29
Q

What isn’t taken into account in the explosive power equation

A

Any negative signs relating to the Q are ignored as we only need the magnitude

30
Q

What is the equation for explosive power?

A
  • Heat x Volume of Gas
  • Q x V
31
Q

What does a negative Q value imply?

A
  • It implies the reaction is exothermic
  • Heat is given to the surroundings rather than removed
32
Q

What order of magnitude should you expect for explosive power?

A

10 5 or 106 or 107 at the most is the value you should expect for these eqs

33
Q

What does a high heat of explosion usually mean?

A

High heat of explosion means you usually have a high power

34
Q

What are mixed explosives used for?

A

Mixed explosives are used to optimise the performance of each component

35
Q

What is the problem with TNT as an explosive?

A

It is very oxygen deficient

36
Q

Why is aluminium added to Torpex?

A
  • Aluminium is added because it has a high enthalpy of combustion and increases the length of the blast weave
  • Aluminium scavenges oxygen atoms from the gaseous products which increases the enthalpy of detonation
  • It is cheap and easy to incorporate
37
Q

What’s the problem with adding aluminium to Torpex?

A
  • Too much aluminium would be counter-productive as it reduces the volume of gas formed
  • Aluminium likes to take oxygen away but its optimised to give the properties we want without taking away too much oxygen.
38
Q

What is thermite usually used for?

A
  • Incendiary weapons
  • Thermite is usually aluminium and iron oxide
39
Q

When are the modified K-W rules applied?

A
  • When the oxygen balance is higher than -40%
  • > -40%
40
Q

What are the modified K-W rules?

A
  1. H atoms to form H2O
  2. C atoms to form CO
  3. If C atoms remaining (and no O) for solid C
  4. N atoms to form N2
41
Q

What are the normal K-W rules?

A
  1. C atoms to form CO
  2. H atoms to form H2O
  3. CO moles form CO2
  4. N atoms to form N2
42
Q

What is changed in the modified K-W rules?

A
  • The way the carbon and hydrogen are consumed is switched
  • This is done to avoid the production of hydrogen
43
Q

What should you include when writing the equation using the K-W rules?

A

The state symbols for the molecules

Fires & Explosions (18 decks)

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