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developing fuels > DF 1 - getting energy from fuels > Flashcards

DF 1 - getting energy from fuels Flashcards

specification reference (d) and (f)

1
Q

what is fuel economy

A

the relationship between the distance travelled and the amount of fuel consumed by a vehicle

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2
Q

what is fuel economy meausured in

A

miles per gallon

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3
Q

why do modern cars have a higher fuel economy than older cars

A

due to improvements in technology

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4
Q

which vehicles have a better fuel economy than petrol and diesel only

A

hybrid and electric vehicles

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5
Q

why is petrol a highly concentrated energy source

A

the amount of energy released per gram of petrol is high compared to many other fuels

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6
Q

what is thermochemistry

A

the study of the enrgy and heat associated with chemical reactions. different fuels give out different amount of energy when one mole is burnt

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7
Q

when can fuels release energy

A

when they have combined with oxygen

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8
Q

what is the energy source for fuels

A

the fuel oxygen systems that provide oxygen for the fuel

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9
Q

what is chemical energy

A

a special form of potential energy that lies within chemical bonds. chemical bonds are the forces of attraction that bind together the atoms in compounds. when chemical react to form new substances, bonds break in the reactants and new bonds are formed as products are made.

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10
Q

what is a characteristic feature of chemical reactions

A

energy changes

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11
Q

what is an exothermic reaction

A

a reaction that gives out energy and heats the surroundings

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12
Q

what is an endothermic reaction

A

a reaction that takes in energy and cools the surroundings

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13
Q

what happens during an exothermic reaction

A

the chemical reactants are losing energy to the surroundings. the energy is used to heat the surroundings. the products end up with less energy than the reactants but the surroundings end up with more and get hotter

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14
Q

what happens during an endothermic reaction

A

the reactants take in energy from the surroundings leaving the products at a higher energy level than the reactants

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15
Q

what is enthalpy

A

the heat content that is stored in a chemical system

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16
Q

what can we measure during a chemical reaction

A

the energy absorbed or released to the surroundings

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17
Q

how can we apply the law of conservation of energy to enthalpy

A

if heat is released, the amount of energy that leaves a chemical system is exactly the same as the amount that goes into the surroundings. no heat energy is lost

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18
Q

what is meant by enthalpy change

A

the energy transferred to and from the surroundings at constant pressure

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19
Q

give the equation to work out enthalpy change

A

enthalpy of products - enthalpy of reactants

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20
Q

where can enthalpy changes be shown

A

on an enthalpy level diagram

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21
Q

give an example of an exothermic reaction

A

combustion of hydrocarbons

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22
Q

give an example of an endothermic reaction

A

decomposition of calcium carbonate

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23
Q

how do measure the enthalpy of a substance

A

by measuring the change in enthalpy when a reaction occurs

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24
Q

what does the enthalpy change of a reaction determine

A

the quantity of energy transferred to or from the surroundings when the reaction is carried out in an open container

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25
Q

what is the unit for enthalpy change

A

kJ per mole

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26
Q

which reaction has a negative enthalpy change and why

A

exothermic - energy is lost to the surroundings
the enthalpy of the products is smaller than the enthalpy of the reactants

27
Q

which reaction has a positive enthalpy change

A

endothermic - energy has been gained from the surroundings
the enthalpy of the products is greater than the enthalpy of the reactants.

28
Q

what is difference between a system and the surroundings

A

the system refers to the reactants and the products of the reaction (the system can lose or gain enthalpy)
the surroundings refer to the “rest of the world” e.g. the tube, the air

29
Q

what is activation energy

A

The activation energy is the minimum amount of energy that particles require in order for a successful collision to occur which will cause the reaction to happen. it is required to break the bonds in the reactants

30
Q

how is the activation energy supplied to the reactants

A

by heating or adding a spark to them

31
Q

what can happen once the energy barrier has been overcome in chemical reactions

A

the net output of energy provides more energy that can used to overcome the activation energy for the reaction to continue

32
Q

how can the enthalpy change vary

A

depending on the conditions in particular temperature, pressure and concentration of solutions

33
Q

what are standard conditions

A

set conditions allowing us to compare enthalpy changes

34
Q

how do elements exist in their standard conditions

A

in their standard states

35
Q

what are standard states

A

the physical stage of a substance under standard conditions

36
Q

what are the standard conditions chosen to compare enthalpy changes

A

a specified temperature normally chosen as 298K (25 degrees celsius)
a standard pressure of 1 atm (1.01 x10 (to the power of 5))
a standard concentration of 1 mol dm -3 for solutions

37
Q

symbol for enthalpy change under standard conditions

A

ΔH°

38
Q

what is the Kelvin K

A

the unit of absolute temperature. the Kelvin is the SI (international system) unit of temperature `

39
Q

what is 0K also called

A

absolute zero

40
Q

do thermometers measure in degress celsius or Kelvin

A

degrees Celsius

41
Q

how to convert from °C to K

A

add 273

42
Q

how to convert from K to °C

A

subtract 273

43
Q

how can enthalpy changes be measured in the lab

A

by arranging for the energy involved in a reaction to be transferred to or from water surrounding the reaction vessel
if the reaction is exothermic —> the water gets hotter
if the reaction is endothermic —> the water gets colder

44
Q

how else can enthalpy changes be measured

A

using the equation of q=mc∆T
energy transferred = mass x specific heat capacity of water (4.18Jg-1K-1) x change in temperature

45
Q

what is calorimetry

A

Calorimetry is the process of measuring the amount of heat released or absorbed during a chemical reaction. By knowing the change in heat, it can be determined whether or not a reaction is exothermic (releases heat) or endothermic (absorbs heat).

46
Q

what is the method for calorimetry

A

1) clamp the metal can at a suitable height to allow room for the spirit burner to be placed below (2-5cm between the base of the can and the top of the spirit burner)
2) fill the metal can with 100cm3 of water
3) measure and record the initial temperaute of the water using a thermometer
4) weigh the spirit burner (and cap) containing the fuel and record the initial mass
5) place the spirit burner on the heat resistant mat under the metal can, remove the cap and light the wick
6) allow the fuel to heat the water so the temperature rises by about 15-20°C
7) use the cap to extinguish the flame
8) record the final temeprature of the water and work out the temperature change
9) reweigh the spirit burner and cap. work out the change in mass/mass of fuel used

47
Q

how do we use the heat equation to work out the energy transferred per mole

A

temperature change and the change in mass/mass of fuel used have already been work out
substitute them into the heat equation along with the specific heat capacity of water to work out the energy transferred
then work out the moles of the fuel by using mass of fuel used and divide it by the mr
then do energy transferred/moles to get energy transferred per mole

48
Q

what are the sources of the error in the calorimetry experiment and how to reduce them

A

in enthalpy experiments that use simple apparatus, it is difficult to avoid energy being transferred to the surroundings. we need to make assumptions when calculating energy changes that are small in comparison with the energy transferred to the water

49
Q

how to improve the calorimetry experiment

A
  • ignore the heat transfer to metal can. metals have a specific heat capacity of 1/10 of water. their masses are small compared to the masses of liquids involved. its also a good insulator
  • ignore energy transfers to any solids in the metal can
  • just consider the water when heating or reacting solutions
  • use a bomb calorimeter
50
Q

what does a bomb calorimeter do

A

in a bomb calorimeter, the fuel is ignited electrically and burns in oxyegn inside the pressurised vehicle. energy is transferred to the surrounding water where the rise in temperature is measured. the experiment is done at constant volume in a closed container

51
Q

what is the standard enthalpy change for a reaction

A

the enthalpy change when molar quantities of reactants react together under standard conditions. this means at 1 atm and 298K with all the substances in their standard states

52
Q

what are the units for the standard enthalpy change of a reaction

A

kJ per mole

53
Q

what is the standard enthalpy change of combustion

A

the enthalpy change that occurs when one mole of a substance is burnt completely in oxygen under standard conditions in standard states

54
Q

why does heptane have a higher enthalpy change value than methane

A

it involves breaking and making more bonds than burning methane

55
Q

why is the enthalpy change of combustion always negative

A

all combustion reactions are exothermic

56
Q

what is the standard enthalpy change of formation

A

the enthalpy change when one mole of a compound is formed from its elements under standard conditions in standard states

57
Q

is the standard enthalpy change of formation positive or negative

A

it can be either

58
Q

what is the standard enthalpy change of formation of a pure element in its standard state

A

zero

59
Q

how do we work out the values for the standard enthalpy change of formation

A

we can’t measure them directly so we measure them indirectly making use of quantities that can be measured and incorporating them into an enthalpy cycle

60
Q

what is the standard enthalpy change of neutralisation

A

the enthalpy change when one mole of hydrogen ions react with one mole of hydroxide ions to form one mole of water under standard conditions in solution containing 1 mol dm-3

61
Q

how else is the standard enthalpy change of neutralisation defined

A

per mole of water formed

62
Q

method for the standard enthalpy change of neutralisation practical

A

1) place a polystyrene cup in a 250cm3 glass beaker
2) rinse the measuring cylinder with the 1.0mol dm-3 hydrochloric acid and then measure 25cm3 of 1.0mol dm3 HCl acid and transfer the acid into the polystyrene cup
3) rinse a 2nd measuring cylinder with 1.0moldm3 NaOH solution, then measure 25cm3 of NaOH solution but do not add this to the cup yet
4) start your timer and record the initial temperature of the acid
5) record your temperature of the acid at 1,2,3 minutes. stir the acid immediately before reading the thermometer
6) at the 4th minute, do not record the temperature. instead, add the NaOH and stir
7) continue to stir the solution and then record the temperature at 5,6,7,8,9 and 10 minutes

63
Q

how would we use the results from the neutralisation practical

A

using the heat equation

developing fuels (11 decks)

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