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Isooctane (2,2,4-trimethylpentane) is an important component of petrol used in

cars.

When isooctane is burned, the enthalpy change is −47.8 kJ g−1

Isooctane is a liquid at room temperature with a density of 0.692 g cm−3

Calculate the heat energy released, in kJ, when 1.00 dm3 of isooctane burns in

excess oxygen.

Give your answer to the appropriate number of significant figures.

cars.

When isooctane is burned, the enthalpy change is −47.8 kJ g−1

Isooctane is a liquid at room temperature with a density of 0.692 g cm−3

Calculate the heat energy released, in kJ, when 1.00 dm3 of isooctane burns in

excess oxygen.

Give your answer to the appropriate number of significant figures.

Here is my working https://ibb.co/gckG0y

The best way to solve this is to think about the units. For example if density if g PER cm^3 then multiplying it by the volume (cm3) gives grams (mass).

Even if you don't know the entire method to get the end result, work your way towards such quantities by looking at your units.

The best way to solve this is to think about the units. For example if density if g PER cm^3 then multiplying it by the volume (cm3) gives grams (mass).

Even if you don't know the entire method to get the end result, work your way towards such quantities by looking at your units.

(edited 5 years ago)

Original post by splitter2017

Here is my working https://ibb.co/gckG0y

The best way to solve this is to think about the units. For example if density if g PER cm^3 then multiplying it by the volume (cm3) gives grams (mass).

Even if you don't know the entire method to get the end result, work your way towards such quantities by looking at your units.

The best way to solve this is to think about the units. For example if density if g PER cm^3 then multiplying it by the volume (cm3) gives grams (mass).

Even if you don't know the entire method to get the end result, work your way towards such quantities by looking at your units.

I really dont understand density at all in chemistry as theres no mention at all in the workbook and i cant find it anywhere online, is it possible you could give some basic examples like the units and what they mean? Maybe a pattern which i could apply to other questions, Thank you so much for the solution!

Original post by splitter2017

Here is my working https://ibb.co/gckG0y

The best way to solve this is to think about the units. For example if density if g PER cm^3 then multiplying it by the volume (cm3) gives grams (mass).

Even if you don't know the entire method to get the end result, work your way towards such quantities by looking at your units.

The best way to solve this is to think about the units. For example if density if g PER cm^3 then multiplying it by the volume (cm3) gives grams (mass).

Even if you don't know the entire method to get the end result, work your way towards such quantities by looking at your units.

so density is g per cm^3 and to get just g by itself you times by the volume which is in cm^3

Could you also explain how you used the mass and the enthalpy change to find the energy released, is this a formula ?

Here you are, I have made a summary of the equations that we use in chemistry including the density one.

I have some other summaries on my website if needed http://tdck.weebly.com/chemistry.html but I think the one I attached is what you are after

I have some other summaries on my website if needed http://tdck.weebly.com/chemistry.html but I think the one I attached is what you are after

(edited 5 years ago)

Original post by sohaail23

so density is g per cm^3 and to get just g by itself you times by the volume which is in cm^3

Could you also explain how you used the mass and the enthalpy change to find the energy released, is this a formula ?

Could you also explain how you used the mass and the enthalpy change to find the energy released, is this a formula ?

For the enthalpy change.

The units the question gave was kilo (x 1000) Joules PER gram (g) and so I multiplied this by the mass.

i.e. if there are 692g and we know the enthalpy change is -47800 J for every gram then multiply the two gives you the enthalpy change for all 692 g of the substance.

It can be helpful to draw a triangle like the ones shown in my summary sheet.

Original post by splitter2017

For the enthalpy change.

The units the question gave was kilo (x 1000) Joules PER gram (g) and so I multiplied this by the mass.

i.e. if there are 692g and we know the enthalpy change is -47800 J for every gram then multiply the two gives you the enthalpy change for all 692 g of the substance.

It can be helpful to draw a triangle like the ones shown in my summary sheet.

The units the question gave was kilo (x 1000) Joules PER gram (g) and so I multiplied this by the mass.

i.e. if there are 692g and we know the enthalpy change is -47800 J for every gram then multiply the two gives you the enthalpy change for all 692 g of the substance.

It can be helpful to draw a triangle like the ones shown in my summary sheet.

I dont know how ive gone through 2 years of chemistry without knowing those conversions ! Thank you for your help with everything i really appreciate it!

Original post by sohaail23

I dont know how ive gone through 2 years of chemistry without knowing those conversions ! Thank you for your help with everything i really appreciate it!

What spec is that question from :?

Original post by Nettled

What spec is that question from :?

Aqa, it was from the June 2017 As paper i did last year.

Original post by splitter2017Here is my working https://ibb.co/gckG0y

The best way to solve this is to think about the units. For example if density if g PER cm^3 then multiplying it by the volume (cm3) gives grams (mass).

Even if you don't know the entire method to get the end result, work your way towards such quantities by looking at your units.

The best way to solve this is to think about the units. For example if density if g PER cm^3 then multiplying it by the volume (cm3) gives grams (mass).

Even if you don't know the entire method to get the end result, work your way towards such quantities by looking at your units.

hiii this might sound dumb but i thought cm3 to dm3 was / 10000

google conversions?

Original post by sohaail23

Isooctane (2,2,4-trimethylpentane) is an important component of petrol used in

cars.

When isooctane is burned, the enthalpy change is −47.8 kJ g−1

Isooctane is a liquid at room temperature with a density of 0.692 g cm−3

Calculate the heat energy released, in kJ, when 1.00 dm3 of isooctane burns in

excess oxygen.

Give your answer to the appropriate number of significant figures.

cars.

When isooctane is burned, the enthalpy change is −47.8 kJ g−1

Isooctane is a liquid at room temperature with a density of 0.692 g cm−3

Calculate the heat energy released, in kJ, when 1.00 dm3 of isooctane burns in

excess oxygen.

Give your answer to the appropriate number of significant figures.

hey, if you multiply the gcm-3 by 1000 you get 692g then multiply that the enthalpy change (47.8) which= 33077.6 and 33100 which is the ANS of the mark scheme

- alevel choices
- Biology and chemistry
- What course can I do with psychology , chemistry and spanish a-level?
- Is Chemistry, Physics, Maths and Further Maths a good combo?
- I want to do mechanical engineering.
- I want to do chemical engineering but I applied for chemistry on UCAS
- is it a good choice to take biology physics further maths without chem?
- Will I have the right A level subjects?
- Is chemistry a level hard?
- Summer internship for A level graduates
- Chemistry AQA A level Practice papers
- how hard are these subjects ?
- Can I still get into pharmacy?
- Free ocr biology and chemistry book
- Alevel Chemistry Topic question websites?
- Urgent Help!! MEDICINE AND GCSEs
- C in Biology and D in Chem, while I resit could I do an intensive alevel in maths
- Biomedical science undergrad help! - y13
- medicine
- advice on picking chemistry alevel?

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