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6. (a) Define (i) hydrocarbons, (ii) structural isomers - Leaving Cert Chemistry - Question 6 - 2009
Question 6
6. (a) Define (i) hydrocarbons, (ii) structural isomers. (b) Give a use for the kerosene fraction obtained when crude oil is fractionated. (c) Straight chain molec... show full transcript
Worked Solution & Example Answer:6. (a) Define (i) hydrocarbons, (ii) structural isomers - Leaving Cert Chemistry - Question 6 - 2009
Step 1
Define (i) hydrocarbons
Answer
Hydrocarbons are compounds composed solely of carbon (C) and hydrogen (H) atoms. They can be categorized into different types, such as saturated (alkanes) and unsaturated (alkenes and alkynes), based on their bonding. Saturated hydrocarbons contain single bonds between carbon atoms, while unsaturated hydrocarbons contain at least one double or triple bond.
Step 2
Define (ii) structural isomers
Answer
Structural isomers are compounds that have the same molecular formula but differ in the arrangement of atoms. This variation leads to distinct chemical and physical properties. Structural isomers can exhibit differences in branching, connectivity, and functional groups.
Step 3
Give a use for the kerosene fraction obtained when crude oil is fractionated
Answer
The kerosene fraction, commonly used as aviation fuel, serves essential functions in aviation. Its high energy content and specific properties make it ideal for powering jet engines, contributing to safe and efficient flight operations.
Step 4
Step 5
Step 6
Name two other processes carried out in oil refineries to modify hydrocarbon structures
Answer
Two other processes used in oil refineries to modify hydrocarbon structures are:
- Reforming: This process rearranges hydrocarbon molecules to improve the quality of gasoline.
- Hydrocracking: In this method, large hydrocarbons are broken down into lighter, more useful fractions in the presence of hydrogen.
Step 7
Calculate the heat of formation of this C₈H₁₈ isomer
Answer
Using Hess's law, the heat of formation can be calculated based on the given equation:
For the reaction:
ightarrow 8 ext{CO}_2 + 4 ext{H}_2 ext{O} \ ΔH = -2710 ext{ kJ mol}^{-1}$$ We can express the heat of formation for C₈H₁₈ as follows: 1. The formation of products: - $8 imes (-394)$ (for CO₂) \ - $4 imes (-286)$ (for H₂O) \ 2. Thus, applying the formula: - $$ΔH = ext{Total Heat of Products} - ext{Heat of Formation of Reactants}$$ - $$ΔH = [-2710] - [8 imes (-394) + 4 imes (-286)]$$ - Therefore, calculate: - $$ΔH = -2710 - [-3152 -1144]$$ - Finally, solve for the heat of formation of the C₈H₁₈: - So, compute and write the final value.