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A LEVEL CHEM > MOD 3 Chap 3.2 > Flashcards

MOD 3 Chap 3.2 Flashcards

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1
Q

define:

system-
surroundings-
universe-

A

system- the chemicals (reactants and products)

surroundings- the apparatus/classroom-anything not involved in reaction

universe- systems+ surroundings

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2
Q

enthalpy change= H(…) - H(…)

A

enthalpy change= H(products) - H(reactants)

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3
Q

bond making is e…thermic
bond breaking is e…thermic

A

bond making is exothermic
bond breaking is endothermic

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4
Q

If more energy is needed to break bonds than given out when making bonds the reaction is e- thermic

A

endothermic

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5
Q

if less energy is needed in breaking bonds than given out when making bonds the reaction is e- thermic

A

exothermic

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6
Q

enthalpy change in exothermic reactions is (positive/negative)

A

enthalpy change in exothermic reactions is negative

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7
Q

enthalpy change in endothermic reactions is (negative/positive)

A

enthalpy change in endothermic reactions is positive

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8
Q

define average bond enthlpy

A

the energy required to break one mole of a specified type of bond in a gaseous molecule

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9
Q

limitations of using average bond enthalpies

A

actual bond enthalpy can vary on the chemical environment of the bond

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10
Q

state the factors affecting the rate of chemical reactions

A

temperature
pressure
concentration
surface area
addition of a catalyst

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11
Q

the collision theory states that for 2 molecules to react they must first ________. this collision must have ______ ________ to overcome the activation energy of the reaction and the reaction must have the correct ______________

A

the collision theory states that for 2 molecules to react they must first collide. This collision must have sufficient energy to overcome the activation energy of the reaction and the reaction must have the correct orientation

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12
Q

describe the effect of concentration on reaction rate

A

increased concentration gives more molecules in the same volume…

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13
Q

the law of conservation of energy states

A

that energy cannot be created or destroyed, only moved from one place to another.

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14
Q

△H= __________ - _______________

A

△H= H products-H reactants

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15
Q

in exothermic reactions the enthalpy on the products is _________ than the enthalpy of the reactants. △H has a +/- sign because energy has been _______ by the chemical system

A

in exothermic reactions the enthalpy on the products is smaller than the enthalpy of the reactants. △H has a - negative sign because energy has been lost by the chemical system

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16
Q

in an endothermic reaction the enthalpy of the products is _________ than the enthalpy of the reactants. △H has a +/- sign because heat has been _______ by the chemical system

A

in an endothermic reaction the enthalpy of the products is greater than the enthalpy of the reactants. △H has a + positive sign because heat has been gained by the chemical system

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17
Q

define activation energy

A

the minimum energy required to start a reaction by breaking bonds in the reaction

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18
Q

identify the standard conditions

A

100kPa
273K (+273 to go from C to K)
1 mol/dm3

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19
Q

Define the enthalpy change of formation

A

the enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions, with all reactants and products in their standard states.

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20
Q

Define the enthalpy change of combustion

A

the enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions with all the reactants and products in their standard state.

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21
Q

define the enthalpy change of neutralisation

A

enthalpy change that accompanies the reaction of an acid by a base to form one mole of water molecule under standard conditions with all reactants and products in their standard states.

the value of the enthalpy change of neutralisation is the same for all neutralisation reactions.
-57 kJmol-1

22
Q

△neutH =______

A

△neut H= -57kJmol-1

23
Q

the specific heat capacity of water is _________

A

4.18 Jg-K-

24
Q

calorimetry is…

A

calorimetry is the quantitative study of energy in a chemical reaction

25
Q

define specific heat capacity

A

the energy required to raise the temperature of 1g of a substance by 1 K

26
Q

Hess’s law states that

A

if a reaction can take place by more than one route and the initial and final conditions are the same the total enthalpy change is the same

27
Q

sum of clockwise arrows= ___________

A

sum of clockwise arrows= sum of anticlockwise arrows

28
Q

The collision theory states. . .

A

For 2 molecules to react they must collide in the correct orientation with sufficient energy to overcome the activation energy

29
Q

How does concentration affect rate of reaction

A

increased con. gives more molecules in the same given volume

Molecules will be closer together higher chances of them colliding with sufficient energy to overcome the activation energy.

More frequent collisions

30
Q

How does pressure affect reaction rate

A

when pressure in gas is increased molecules are pushed closer together.

Same number of molecules occupies a smaller volume
gaseous increase in pressure is the same thing as increasing con.

more collisions likely to occur with sufficient energy to overcome activation energy

Therefore
rate increases with pressure

31
Q

A _____________ can be used to monitor changes in concentrations of coloured reactants/products

A

A COLORIMETER can be used to monitor changes in concentrations of coloured reactants/products

32
Q

define catalyst

A

a substance that increases the rate of reaction without being used up in the process.

33
Q

How does a catalyst increase rate of chemical reactions

A

A catalyst lowers the activation energy by providing an alternative route for the reaction to follow.

34
Q

Describe the effect of temperature on rate of reaction

A

Increasing temperatures increases the kinetic energy of all the molecules. The Boltzmann distribution flattens and shifts to the right.

35
Q

the Boltzmann Distributions shows . . .

A

the distribution of energies of molecules at a particular temperature- shown on a graph

35
Q

What happens to the area under the Boltzmann curve when temperature is increased

A

The area remains the same as the number of molecules in the system stays the same.

36
Q

A chemical system is in dynamic equilibrium when . . .

A

The concentration of reactants and products remains constant.

The rate of the forward reaction is the same as the rate of the reverse reaction.

37
Q

Define Le Chateliers principle

A

If dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change

38
Q

state the factors affecting the position of equilibrium

A

pressure
concentration
temperature

39
Q

pressure in a system will only change the position of equilibrium if the state is ___________

A

pressure in a system will only change the position of equilibrium if the state is gaseous

40
Q

Increasing the total pressure of the system causes the position of equilibrium to move to the side with __________ gas molecules.

A

Increasing the total pressure of the system causes the position of equilibrium to move to the side with fewer gas molecules.

41
Q

Increasing the pressure of one of the gases in the system is the same as increasing ________________

A

Increasing the pressure of one of the gases in the system is the same as increasing CONCENTRATION

42
Q

The hotter the reaction the more likely its equilibrium to shift to the _________ direction.

A

The hotter the reaction the more likely its equilibrium to shift to the endothermic direction to take in energy to decrease temp.

43
Q

name 2 types of catalysts

A

Homogeneous catalyst
Heterogeneous catalyst

44
Q

Explain what is meant by a HOMOGENOUS catalyst

A

The catalyst has the same physical state as the reactants

It reacts with the reactants to form an intermediate. The intermediate breaks down to give a product. The catalyst is then regenerated.

45
Q

Explain what is meant by a HETEROGENEOUS catalyst

A

The catalyst has a different physical state as the reactants
Usually solids in contact with gaseous reactants or reactants in a solution.

The reactants are absorbed (weakly bonded) to the surface of the catalyst. After the reaction the products leave the surface by desorption

46
Q

give an example of a heterogenous catalyst

A

Catalytic converter-

47
Q

How do catalysts enable sustainability

A

The activation energy needed for the reaction to take place is lowered.

Reaction can now take place at a lower temperature.

Less electricity needed

Less fossil fuels used.

Ultimately saving money for the company and helping reduce harmful greenhouse gas emissions.

48
Q

describe the effect of a catalyst on equilibrium

A

A catalyst does not alter the position of equilibrium or the position of an equilibrium system

49
Q

Drawbacks of using theoretical conditions in relation to equilibrium and yield

A

Low temperature should produce high equilibrium yield.

BUT it would happen at low rate

High pressure increases the concentration of gases increasing the reaction rate- producing both a high equilibrium yield and a high rate.

BUT it also increases costs and there are also safety implications- a failure in the system could cause chemicals to leak into the environment endangering those working on site.

A LEVEL CHEM (10 decks)

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