Lecture 3 Flashcards
Are drop test measurements qualitative or quantitative?
Drop test measurements are semi-quantitative with an arbitrary scale of sensitivity
What is entropy related to?
Related to the volume of gas we generate
What was the issue with gunpowder in the early days?
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.
What is a desirable property of an explosive?
For it to contain oxygen
What is the equation for power?
Power = Q x V
What does Q stand for?
Heat of explosion (enthalpy)
What does V stand for?
Volume of gas in moles
What do Kistiakowsky rules predict?
It predicts the products of an explosion
What does the oxygen balance dictate?
Oxygen balance dictates whether a detonation consumes external O2
What determines the oxygen balance?
The molecular formula determines the oxygen balance
What is the formula to determine the number of oxygen atoms required?
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
How do you calculate oxygen balance as a mole percentage?
Ω = (([d - 2a - b/2] x 16) / molecular weight) x 100
What decimal place should you use for the molecular weight of the explosive in the oxygen balance equation?
To the nearest whole number as the calculation is only an approximation
If you have a negative oxygen balance what does this suggest?
This suggests the molecule is oxygen deficient
What does an oxygen balance of 0 indicate?
This suggests there is exactly enough oxygen to make CO2 and H2O
When are the Kistiakowsky-Wilson rules applied?
- When the oxygen balance is between 0 and -40%
- Oxygen balance is < -40%
What does it mean if the oxygen balance is less than 0?
If the oxygen balance is less than zero the carbon and hydrogen cannot be fully oxidised
What are the K-W rules used to determine?
K-W ‘rules’ can be used to determine what the products of detonation actually are
If the oxygen balance is higher than -40% what rules should be used?
The modified K-W rules
What do the K-W rules prioritise?
It prioritises the use of limited oxygen atoms to form reaction products
Are the K-W rules used for detonation or combustion?
- They are used for detonation
- Combustion is when you use oxygen from the atmosphere
What gaseous product would qualitatively indicate a near-neutral or positive oxygen balance?
CO2 would indicate this as it is the last stop in the KW rules and is only formed when we have oxygen left over.
How do you calculate the enthalpy of detonation? (Q or ΔdH)
Sum of the enthalpy formation of the products - sum of the enthalpy formation of the reactants
What is the enthalpy of formation for compounds in a standard state?
0
What does the volume of detonation depend on?
The volume of detonation depends on the moles of gas released
Other than the volume of detonation, what is the moles of gas a measure of?
The entropy change
What is the volume for one mole of gas?
22.4 1mol-1 as we treat all gases as ideal gases and assume the occupy about the same volume
What is the explosive power a measure of?
The explosive power is a measure of both enthalpic and entropic components of an explosion
What isn’t taken into account in the explosive power equation
Any negative signs relating to the Q are ignored as we only need the magnitude
What is the equation for explosive power?
- Heat x Volume of Gas
- Q x V
What does a negative Q value imply?
- It implies the reaction is exothermic
- Heat is given to the surroundings rather than removed
What order of magnitude should you expect for explosive power?
10 5 or 106 or 107 at the most is the value you should expect for these eqs
What does a high heat of explosion usually mean?
High heat of explosion means you usually have a high power
What are mixed explosives used for?
Mixed explosives are used to optimise the performance of each component
What is the problem with TNT as an explosive?
It is very oxygen deficient
Why is aluminium added to Torpex?
- 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
What’s the problem with adding aluminium to Torpex?
- 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.
What is thermite usually used for?
- Incendiary weapons
- Thermite is usually aluminium and iron oxide
When are the modified K-W rules applied?
- When the oxygen balance is higher than -40%
- > -40%
What are the modified K-W rules?
- H atoms to form H2O
- C atoms to form CO
- If C atoms remaining (and no O) for solid C
- N atoms to form N2
What are the normal K-W rules?
- C atoms to form CO
- H atoms to form H2O
- CO moles form CO2
- N atoms to form N2
What is changed in the modified K-W rules?
- The way the carbon and hydrogen are consumed is switched
- This is done to avoid the production of hydrogen
What should you include when writing the equation using the K-W rules?
The state symbols for the molecules
