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chemistry > module three: chapter nine: enthalpy > Flashcards

module three: chapter nine: enthalpy Flashcards

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1
Q

what is the enthalpy change equation?

A

∆H= H (product)- ∆ (reactant)

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2
Q

how can you tell if ∆H is exothermic?

A

it is negative

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3
Q

how can you tell if ∆H is endothermic?

A

it is positive

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4
Q

what does the conservation of energy mean for exothermic reactions?

A

the chemical system releases heat energy to surroundings,
any energy loss by the system is balanced by the same energy gain by surroundings,
the temperature of surroundings increases as they gain energy.

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5
Q

what does the conservation of energy mean for endothermic reactions?

A

the chemical system takes in heat energy from surroundings,
any energy gain by the system is balanced by the same energy loss from surroundings,
the temperature of surroundings decreases as they lose energy.

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6
Q

what is activation energy? (Ea)

A

the minimum energy required for a reaction to take place

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7
Q

what are the standard conditions?

A

standard pressure: 100kPa
standard temperature: 298K
standard concentration: 1moldm-³

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8
Q

what is the standard enthalpy change of reaction? ∆rH

A

the enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions, with all reactants and products in their standard states.

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9
Q

what are example equations showing ∆rH?

A

Mg+ ½O2→ MgO
2Mg+ O2→ 2MgO

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10
Q

what is standard enthalpy change of formation? ∆fH

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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11
Q

what is an example equation showing enthalpy change of formation?

A

Mg+ ½O2→ MgO (∆fH for MgO)

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12
Q

what is the standard enthalpy change of combustion? ∆cH

A

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

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13
Q

what is an example equation to show ∆cH?

A

C4H10+ 6½O2→ 4CO2+ 5H2O

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14
Q

what is standard enthalpy change of neutralisation? ∆neutH

A

the energy change that accompanies the reaction of an acid by a base to form one mole of H2O under standard conditions with all reactants and products in their standard states

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15
Q

what are example equations to show ∆neutH?

A

H+ + OH- →H2O
HCl + NaOH →H2O + NaCl

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16
Q

what is the equation to calculate energy change?

A

q=mc∆T

17
Q

what does q mean q=mc∆T?

A

heat energy

18
Q

what does m mean in q=mc∆T?

A

mass

19
Q

what does c mean in q=mc∆T?

A

specific heat capacity

20
Q

what does ∆T mean in q=mc∆T?

A

temperature change

21
Q

what is the pag for determination of enthalpy change of combustion?

A
  1. measure out 150cm³ water into a beaker, record initial temperature.
  2. add methanol to the spirit burner, weigh it.
  3. place the burner under the beaker, light the burner and burn methanol while stirring the water with thermometer.
  4. after three minutes extinguish the flame, immediately record max temperature of water.
  5. reweigh spirit burner
22
Q

how do you determine the enthalpy change of reaction?

A
  1. pipette 25cm³ of 1moldm-³ CuSO4 into a polystyrene cup, weigh excess zinc powder.
  2. start stop watch and take temp of solution every 30s until temp stays constant.
  3. add zinc to solution and stir, record temp every 30 secs until it has fallen
  4. plot a graph and extrapolate
23
Q

what is average bond enthalpy?

A

the energy required to break one mole of a specified type of bond in a gaseous molecule. energy is always required to break bonds, bond enthalpies are always endothermic.

24
Q

is it endothermic to break or make bonds?

A

break, as energy is required

25
Q

is it exothermic to break or make bonds?

A

make, as energy is released

26
Q

what is the equation for calculating enthalpy change from average bond enthalpies?

A

∆rH = bond enthalpies in reactants - bond enthalpies in products

27
Q

what is hess’s law?

A

if a reaction takes place by two routes and the starting and finishing conditions are the same, the total enthalpy change is the same for each route.

chemistry (7 decks)

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