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Chemistry > Paper 1 > Flashcards

Paper 1 Flashcards

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1
Q

What is mean bond enthalpy?

A

measure the enthalpy change when one mole of bonds are broken, taken as an average from a range of different compounds.

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2
Q

What is bond dissociation enthalpy?

A

the enthalpy change when one mole of a bond is broken to give separated atoms with everything in the gas phase or gas state or gaseous state .

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3
Q

What is standard enthalpy of formation?

A

the enthalpy change when one mole of a substance is formed from its constituent elements in their standard states under standard conditions.
(exothermic)

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4
Q

What is first ionisation energy?

A

the energy required to remove one mole of electrons from one mole of gaseous atoms of that element.
(endothermic)

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5
Q

What is second ionisation energy?

A

the energy required to remove one mole of electrons from one mole of gaseous 1+ ions of that element.
(endothermic)

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6
Q

What is the enthalpy of lattice dissociation?

A

the enthalpy change when one mole of an ionic solid is transformed into its gaseous ions.

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7
Q

What is the enthalpy of lattice formation?

A

the enthalpy change when one mole of an ionic lattice is formed from its constituent gaseous ions.

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8
Q

What is the standard enthalpy change of atomisation?

A

the enthalpy change when one mole of gaseous atoms is formed from an element in its standard state under standard conditions.
(endothermic)

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9
Q

Why are first electron affinities exothermic, but the rest endothermic?

A

1st electron affinities are exothermic because the overall force between an external electron and a nucleus is attractive .

2nd and higher electron affinities are endothermic because the overall force between an external electron and a negatively charged ion is repulsive .

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10
Q

What is a covalent bond?

A

the strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.

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11
Q

What is an ionic bond?

A

an electrostatic force of attraction between a cation and an anion.

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12
Q

What is a metallic bond?

A

the strong electrostatic force of attraction between the metal ions and the delocalised electrons.

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13
Q

What is the enthalpy change of solution?

A

the enthalpy change when one mole of a solute, in its standard state, dissolves in water to form aqueous ions.

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14
Q

Is the enthalpy of hydration exothermic or endothermic?

A

always exothermic.

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15
Q

What is an instantaneous reaction?

A

the rate of reaction at a particular point in time.

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16
Q

Describe Emp (Maxwell-Bolztmann distribution).

A
  • Emp represents the most probable energy in a sample of gas.
  • Emp is the energy that a randomly selected particle is likely to have .
  • Emp is the energy at the peak of a Maxwell-Bolztmann curve.
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17
Q

Describe how a homogeneous catalyst works to increase the rate of a reaction.

A
  • provide an alternative reaction route, with lower activation energy than the original reaction, causing the reaction rate to increase.
  • done by reacting to form an intermediate, which reacts further to form the final products of the reaction.
  • the catalyst is regenerated, meaning that it is not used up during the reaction.
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18
Q

How does a heterogeneous catalyst increase the rate of reaction?

A
  • reactant molecules adsorb to the surface of the catalyst at an active site.
  • the reaction takes place on the surface of the catalyst.
  • the products detach from the catalyst’s surface in a process called desorption.
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19
Q

How do you work out how Q affects the rate of reaction (in terms of its order):

Q + R + S –> T + U

A

complete the reaction with excess R and S (as it maintains their concentrations over the course of the reaction) to see how a change in the concentration of Q changes the rate of the reaction.

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20
Q

In a concentration-time graph what does a straight, diagonal line indicate?

A

that the reactant is in 0th order.

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21
Q

In a concentration-time graph what does a curved line indicate?

A

that the reactant in 1st or 2nd order.

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22
Q

Describe how a rate-concentration graph represents the different orders.

A

0th order:
- a straight, horizontal line.

1st order:
- a straight, diagonal line from 0.

2nd order:
- a curved line from 0.

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23
Q

What are elementary steps?

A

basic steps in a reaction that can’t be broken down any further.

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24
Q

What is a reaction mechanism?

A

the sequence of elementary steps that actually occur during a reaction.

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25
Q

How do you work out the rate-determining step?

A

1) First, look for the slowest step in the reaction.
2) Second, cross out the intermediates.
3) Third, write down the reactant molecules involved before and during the slowest step.
4) Fourth, add these reactant molecules to the rate equation, using powers if you need to.

26
Q

What is the rate-determining step?

A

the slowest elementary step in a reaction, which determines the rate of the reaction.

27
Q

Why does increasing the volume of water in a flame calorimeter improve the accuracy of the results?

A
  • larger the mass of water, means a smaller the increase in temperature during the reaction.
  • if water is closer in temperature to the surrounding air, less heat energy escapes.
  • more of the heat energy released from burning the fuel is transferred to the water.
  • the heat energy we measure transferred the water is more accurate as less is lost to the surroundings.
28
Q

Are breaking bonds exothermic or endothermic?

A

endothermic.

29
Q

Are forming bonds exothermic or endothermic?

A

exothermic.

30
Q

When atoms split from a molecule we say they…?

A

dissociate.

31
Q

How do calculate how much energy it takes to break one mole of H2, when you know the amount of energy to break one H-H bond?

A

multiply the amount of individual energy for one bond by Avogadro’s constant.

32
Q

What is bond dissociation enthalpy?

A

the enthalpy change when one mole of a bond is broken to give separated atoms with everything in the gas phase or gas state or gaseous state .

33
Q

What do mean bond enthalpies measure?

A

the enthalpy change when one mole or a mole or 1 mole of bonds is broken, taken as an average from a range of different compounds.

34
Q

What is a limitation of using mean bond enthalpies?

A

because values are taken from a range of different compounds.

35
Q

What does the e^-Ea/RT (from the Arrhenius equation) allow you to calculate?

A

the proportion of particles in a reaction with energy greater than or equal to the activation energy.

36
Q

What can you use the Arrhenius equation for?

A

quantify the relationship between k and T.

37
Q

Why do we rearrange the Arrhenius equation into the form y=mx+c?

A
  • so we can clarify a relationship between T and k.
  • so we can plot a graph showing the relationship between T and k.
38
Q

Describe the relation of the Arrhenius equation to y=mx+c.

A
  • y = ln(k)
  • m = -Ea/R
  • x = 1/T
  • c = ln(A)
39
Q

When Kc > 1, where does the equilibrium position sit?

A

to the right.

40
Q

When Kc < 1, where does the equilibrium position sit?

A

to the left.

41
Q

Which states are expressed in a heterogeneous Kc equation? And why?

A
  • gas
  • aqueous
  • liquid (if more than one liquid)

…because we only include substances whose concentrations can vary during the reaction.

42
Q

How do you calculate total pressure?

A

Total Pressure = p_A+p_B

43
Q

How do you calculate a mole fraction of a gas A?

A

number of moles of gas A / total number of moles of gas in mixture

44
Q

How do you calculate the partial pressure (p_A)?

A

p_A = total pressure x mole fraction A

45
Q

Why are only gases used in a heterogeneous equilibrium reaction for Kp?

A

because only the pressure of gases significantly change during the reaction.

46
Q

When we increase the temperature of a reaction, the value for Kp…

A
  • increases if the forward reaction is endothermic.
  • decreases if the forward reaction is exothermic.
47
Q

What is standard molar entropy?

A

the entropy of one mole of a substance at 298K.

48
Q

What must ‘Delta G’ be for a reaction to be feasible?

A

negative.

49
Q

‘Delta G’ is usually stated with units of…

A

kJmol-1.

50
Q

Is the dissociation of water exothermic or endothermic?

A

endothermic.

51
Q

What happens when the temperature of a reaction ,where water is dissociated, decreases?

A
  • the equilibrium will shift to the left, so the Kw value decreases at lower temperatures.
52
Q

Chase adds 10.00g of calcium hydroxide to 1dm^3 of water at room temperature. He calculates that the pH of the resulting solution should be 13.43. However, when he measures the pH with a pH metre, he gets a lower value. Why?

A
  • If calcium hydroxide were completely soluble, the solution would have a pH of 13.43.
  • However, calcium hydroxide is only slightly soluble in water. Even though 10g of calcium hydroxide was added to water, only a small amount actually dissolves and produces Ca2+ and OH- ions.
  • Therefore, since the OH- in the solution is lower than expected, the H+ will be higher than expected in order to keep the Kw value constant.
  • This higher H+ will cause the measured pH to be lower than 13.43.
53
Q

Does the solubility of group 2 hydroxides increase or decrease down the group?

A

increase.

54
Q

What does an endothermic energy profile look like?

A
  • positive overall energy change.
  • products have more energy (above) than reactants (below).
  • take in energy.
55
Q

What does an exothermic energy profile look like?

A
  • negative overall energy change.
  • products have less energy (below) than reactants (above).
  • give out energy.
56
Q

Why do we use a platinum strip in the hydrogen electrode?

A
  • H2 can’t conduct electricity, so we need a metal strip to conduct electrons.
  • Platinum is used because it conducts electrons, but doesn’t react with anything itself.
57
Q

When would you use a platinum electrode?

A
  • when using a hydrogen electrode.
  • when there are no solid reactants or products.
58
Q

Stronger oxidising agents than H2 will have a ________ electrode potential.

A

positive.

59
Q

Stronger reducing agents than H2 will have a ________ electrode potential.

A

negative.

60
Q

Does a negative electrode potential go on the left or right of the diagram?

A

left.

Chemistry (3 decks)

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