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CH0002 > Thermodynamics I > Flashcards

Thermodynamics I Flashcards

1
Q

What is energy

A

Energy is the capacity to do work

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2
Q

By understanding energy changes what can we predict

A

Which molecules form, what they will react with and to what extent

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3
Q

What is the First Law of Thermodynamics

A

Energy can neither be created nor destroyed, merely transferred into a different form (conservation of energy)

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4
Q

In energy accountancy what two things is the universe made up from

A

They system and surroundings

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5
Q

What is a system in energy accountancy

A

The part of the universe we are interested in e.g. solutions in a beaker, chemical reactor, electrochemical cell

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6
Q

What are the surroundings in energy accountancy

A

Everything else in contact with the system which can influence its state

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7
Q

What type of system is this and describe it in terms of exchange of energy and matter. Give an example

A

Closed system. There is exchange of energy bu not matter with the surroundings. An example is making ice cubes

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8
Q

What type of system is this and describe it in terms of exchange of energy and matter. Give an example

A

It is an open system. There is exchange of both energy and matter with the surroundings. An example is a drying wet washing

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9
Q

What type of system is this and describe it in terms of exchange of energy and matter. Give an example

A

It is an isolated system. There is no exchange of energy and matter with the surroundings. An example is a thermos flask

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10
Q

What is work

A

Work is the transfer of energy causing motion against a force

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11
Q

Explain how this reaction is an example of work being done:

Zn(s) + HCl(aq) -> ZnCl(aq) + H2(g)

A

At constant pressure there is an increase in volume due to the creation of gas showing that the reaction has done work

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12
Q

If work = force x displacement.

But pressure = force/ area or pressure x area = force what does work equal

A

Work = pressure x change in volume

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13
Q

What does δV mean

A

Small change in volume

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14
Q

What does ΔV mean

A

Big change in volume

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15
Q

What is heat

A

Heat is the transfer of energy as a result of temperature difference between the system and surroundings

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16
Q

What is a positive change in heat or work

A

A change in heat or work that increases the energy of the system

17
Q

What does Q stand for

A

Heat

18
Q

What does W stand for

A

Work

19
Q

What does a positive Q value represent

A

Means IN (absorbed by the system)

20
Q

What does a negative Q value represent

A

Means OUT (absorbed by the surroundings)

21
Q

What does a positive W value represent

A

Means DONE ON the system

22
Q

What does a negative W value represent

A

Means DONE BY the system

23
Q

How are heat changes measured

A

By using a calorimeter

24
Q

What is a calorimeter

A

A reaction vessel surrounded by a water bath containing a thermometer

25
Q

What is the equation for heat supplied

A

Q = mwater x Cwater x ΔT

m- mass, c- heat capacity

26
Q

At constant pressure Q equals

A

Q = ΔH (enthalpy change)

27
Q

At constant volume Q equals

A

Q = ΔU (internal energy change)

28
Q

What equation is used to express the 1st Law of Thermodynamics

A

ΔH = ΔU + PΔV

29
Q

What does a negative PΔV value show

A

The system is doing work

30
Q

What does a positive PΔV value show

A

Work is being done on the system

31
Q

What is reaction enthalpy

A

The measured heat change for a reaction at atmospheric pressure

32
Q

Enthalphy is state fucntion, what does this mean

A

That a change in enthalpy depends only on the difference between the starting state and the final state, not the route taken

33
Q

The value for ΔH depends on the number of steps taken. True/ False

A

False. It is the same whether the reaction is carried out in one or several steps

34
Q

What is Hess’s Law

A

The standard enthalpy (ΔH°) of a reaction is the sum of all the standard enthalpies of the reactions into which the overall reaction may be divided, even if this division is artificial.

35
Q

What is the first method for calculating Hess’s Law

A
36
Q

What is the second method for using Hess’s Law

A
37
Q

How would you work out enthaply when given various reactions with enthalpies and then asked to work out the enthalpy of one specific reaction

A
  1. Write out the reaction in full using the given ethaply equations
  2. Cancel out substances which occur on the left and right hand side of the equation
  3. Check if new reaction is the same as unknown enthaply reaction
  4. Add together the enthalpies for the stated reaction
38
Q

What do you need to remember to do if you use the reverse of a stated ethaply reaction

A

To swap the enthaply of a reaction i.e. if it was positive it becomes negative

39
Q

What is standard pressure

A

1 atm (atmosphere)

CH0002 (13 decks)

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