Energy

Question 1

what is ignition temperature?

Answer 1

the minimum temperature required fora combustible fuel to ignite spontaneously

Question 2

what is ignition temperature related to?

Answer 2

activation energy

Question 3

what is activation energy?

Answer 3

the minimum amount of energy required for the reactants to form products in a reaction

Question 4

what are some indicators of a chemical change?

Answer 4

• change in color
• change in smell
• bubbling of a gas
• formation of a precipitate

Question 5

what are some allotropes of carbon ?

Answer 5

diamond 
graphene 
fullerenes 
graphite 
nanotubes

Question 6

what are fossils?

Answer 6

-dead organic matter which has been preserved under the earths crust over many millennia containing traces of the suns energy

this energy is released when these fossils are burnt

Question 7

why can graphite conduct electricity?

Answer 7

some carbon atoms in its lattice do not share their electrons, which forms localized electrons

Question 8

why is diamond so strong?

Answer 8

carbon atoms are arranged tedrahedrally in a covalent network

Question 9

why cant diamond conduct electricity?

Answer 9

all four electrons in each carbon atom a part of a covalent bond, meaning there are no free electrons to carry electric charge

Question 10

what are alkanes?

Answer 10

hydrocarbons which are apart of the homologous series which consist of C-C single bonds. they are known as saturated hydrocarbons

Question 11

what are alkenes?

Answer 11

hydrocarbons apart of the functional group containing C=C bonds. at least one double bond must be present. location of double bond is specified in the name of the alkene.

Question 12

what is an isomer?

Answer 12

a molecule with the same molecular formula but different structural formula to another compound.

eg. pentene is an isomer of cyclopentane

Question 13

are alk-anes/enes polar or non polar?

Answer 13

they are non polar

Question 14

why does the MP and BP of a hydrocarbon increase with increasing chain length?

Answer 14

because the number of regions where dispersion forces can form are increased

Question 15

what is meant by volatility?

Answer 15

volatility of a liquid is its readiness to vaporise or evaporate , especially at ordinary temperatures. volatility decreases with increasing strength of the intermolecular forces

Question 16

what are some safety precautions relating to the storage of hydrocarbons?

Answer 16

• store gas cylinders in strong, regularly maintained gas cylinders ensure taps and fittings maintain a tight seal
• store fuels in well ventilated areas
• prevent use of naked flames(sparks) anywhere near hydrocarbons
• liquid hydrocarbons should be stored in suitably labelled containers with tight seals. openings to these containers should be narrow to limit vapour forming

Question 17

why are there so many carbon compounds?

Answer 17

the carbon atom has 4 valence electrons which can bond in many different configurations and structures

Question 18

how are the components of crude oil separated in industry and name two of them and their uses

Answer 18

Crude oil is separated into its components by fractional distillation. In this technique the crude oil is heated in a fractionating tower. As the mixture is heated the different fractions rise up the tower, condensing into trays at different heights depending on their boiling point. Compounds with lower boiling points rise higher up in the tower. Two compounds obtained in this way from crude oil are octane, used as motor vehicle fuel, and kerosene, used as aviation fuel.

Question 19

name one model, and its benefits

Answer 19

• Molecular model kits were used to make models showing the different types of bonds that can exist between carbon atoms.
• models allowed to see that single CC bonds can rotate, whereas double and triple bonds cannot rotate.

-also allowed us to see that triple CC bonds are shorter than double bonds, and that single CC bonds are the longest.
they were very useful in allowing to visualise objects too small to be seen.

Question 20

whats one a limitation of this model?

Answer 20

models do not show molecular vibrations. They also do not show the true relative size of hydrogen vs carbon atoms

Question 21

how does temperature effect reaction rates?

Answer 21

at room temperature, only a few molecules in a reaction mixture would have enough kinetic energy to meet, collide and form products. this proportion of molecules increases as temperature increases, therefore more collisions between particles can occur at higher temperature

Question 22

how does concentration effect reaction rates?

Answer 22

a greater concentration of a substance means for particles are present in the reaction mixture, increasing the chances for collisions. hence, a greater concentration yields a faster rate of reaction

Question 23

how does surface area effect the rate of reaction?

Answer 23

increasing the surface area of a substance exposes more of its particles for collisions, thus a higher surface area yields a faster rate of reaction