chem question (1 Viewer)

[FlueyGuey111]

 

[chilli 412]

it's B. I have never taken chemistry but i got a real good feeling about this

 

[someth1ng]

C

 

[FlueyGuey111]

C

howd u do it?

 

[someth1ng]

higher concentration = more heat per unit volume.

 

[wizzkids]

All the options use neutralisation of a monoprotic acid by sodium hydroxide. All the reactions form one mole of water per mole of acid and base, therefore the enthalpy change for neutralisation is -57 kJ/mol of water formed, so their molar enthalpy change is almost identical. However, the heat that is liberated is absorbed in raising the temperature of the entire mass of solution. Therefore use less water (more concentrated) and you get a higher temperature rise, as @someth1ng said.

 

[jimmysmith560]

View attachment 37277

Would the following working help?

Step 1: Calculate the amount in mole of ethanol available.



Step 2: Use the heat of combustion value to determine the energy available in the ethanol.







Step 3: Calculate the distance that can be travelled.



The answer is therefore (B).

 

[jimmysmith560]

View attachment 37279

Would the following information help?

The data in the table suggests that

• It will be a liquid at room temperature (with a boiling point of 78.3 °C it will be able to be safely stored as a liquid without major storage and safety concerns that might be associated with having to deal with a gas).
• Ethanol is the only fuel that can be derived from sources other then fossil fuels – it is the only fuel (out of those listed) that can come from a renewable source.
• The heat of combustion information is given in terms of kJ g^-1. This does not take into account the mass of the fuels. A more accurate measure for comparing heat of combustion is kJ mol^-1. To obtain this information multiply the given heat of combustion by the molar mass of the fuel. The approximate results would be:

Fuel​	Heat of Combustion (kJ g^-1)​	Molar Mass (M)	Heat of Combustion (kJ mol^-1)​
Methane	55.6​	16​	889.6​
Propane	50.3​	44​	2213.2​
Octane	47.3​	114​	5392.2​
Ethanol	29.7​	46​	1366.2​

The heat of combustion of ethanol is less than some other fuels, however, it is still an efficient fuel, and has other advantages including being a liquid at room temperature.

Some pros and cons of using ethanol as an alternative fuel include:

Advantages​

Disadvantages​

Oxygenated biofuels, such as ethanol, reduced toxic emissions to the environment. Ethanol burns completely to form water and carbon dioxide. Ethanol can be produced from a renewable source, unlike fossil fuels, which are non-renewable. (Note that ethanol can also be made from fossil fuel sources.) Ethanol burns more cleanly than most fossil fuels, with less carbon deposited in the car engine, allowing spark plugs to last longer. Mixtures of ethanol in petrol boost the octane rating, meaning that the fuel burns more completely and reduces engine knock. Because ethanol is an excellent solvent, deposits that have built up in the engine can dissolve, producing a cleaner system. 10% - 24% of anhydrous ethanol can be added to existing petrol engines without modification to produce a fuel called a gasohol, which can act as a petrol extender. Ethanol has a lower ignition temperature than petrol, so fuel-air combustible mixtures ignite more readily. Ethanol vapour-air mixtures have a greater flammability range than petrol vapour-air mixtures. Thus, rich ethanol-air mixtures will ignite and combust more readily. Ethanol-petrol blends reduce CO emissions by 25% - 30% as well as reducing ozone formation. Ethanol can be relatively cheaply and safely stored and transported as it has a boiling point of 78.3 °C and is therefore a liquid at most temperature ranges in which it is likely to be used.

Existing car engines would need modifications to run on hydrous ethanol, due to potential corrosion caused by the presence of water. Greater engine wear occurs with high ethanol-petrol blends due to the need for higher compression ratios Ethanol has a higher flash point than petrol and so combustible fuel-oxygen mixtures are hard to obtain in cold areas of the world. Large areas of land are needed to grow crops that can be harvested for ethanol production. There is a scarcity of land with availability of water and sunshine for such crops. Food production would also not be possible in such areas. Removal of forests to create such farming land would be ecologically unacceptable. (This problem is reduced if ethanol is produced from waste sources of glucose such as sugar cane pulp). At present, it is more expensive to produce 1 litre of ethanol than 1 litre of super petrol, although there may be more equity in the price in the future as crude oil becomes more expensive due to increasing scarcity or other factors (including disruption to production and war).

 

[wizzkids]

View attachment 37279

You haven't given the number of marks allocated to this question, but from the looks of the limited data, it is probably a 3 or 4-mark question. By the way, there are errors in the data. (1) Propane cannot be sourced from natural gas. (2) Methane is the main component of natural gas, so the table contains two errors.
Anyway, you would have to answer with four solid Chemistry facts about alternative fuels. The action verb is "assess" so you have to give two reasons for and two reasons against.