Thermodynamics I

Question 1

What is energy

Answer 1

Energy is the capacity to do work

Question 2

By understanding energy changes what can we predict

Answer 2

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

Question 3

What is the First Law of Thermodynamics

Answer 3

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

Question 4

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

Answer 4

They system and surroundings

Question 5

What is a system in energy accountancy

Answer 5

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

Question 6

What are the surroundings in energy accountancy

Answer 6

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

Question 7

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

Answer 7

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

Question 8

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

Answer 8

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

Question 9

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

Answer 9

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

Question 10

What is work

Answer 10

Work is the transfer of energy causing motion against a force

Question 11

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

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

Answer 11

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

Question 12

If work = force x displacement.

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

Answer 12

Work = pressure x change in volume

Question 13

What does δV mean

Answer 13

Small change in volume

Question 14

What does ΔV mean

Answer 14

Big change in volume

Question 15

What is heat

Answer 15

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

Question 16

What is a positive change in heat or work

Answer 16

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

Question 17

What does Q stand for

Answer 17

Heat

Question 18

What does W stand for

Answer 18

Work

Question 19

What does a positive Q value represent

Answer 19

Means IN (absorbed by the system)

Question 20

What does a negative Q value represent

Answer 20

Means OUT (absorbed by the surroundings)

Question 21

What does a positive W value represent

Answer 21

Means DONE ON the system

Question 22

What does a negative W value represent

Answer 22

Means DONE BY the system

Question 23

How are heat changes measured

Answer 23

By using a calorimeter

Question 24

What is a calorimeter

Answer 24

A reaction vessel surrounded by a water bath containing a thermometer

Question 25

What is the equation for heat supplied

Answer 25

Q = m_water x C_water x ΔT m- mass, c- heat capacity

Question 26

At constant pressure Q equals

Answer 26

Q = ΔH (enthalpy change)

Question 27

At constant volume Q equals

Answer 27

Q = ΔU (internal energy change)

Question 28

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

Answer 28

ΔH = ΔU + PΔV

Question 29

What does a negative PΔV value show

Answer 29

The system is doing work

Question 30

What does a positive PΔV value show

Answer 30

Work is being done on the system

Question 31

What is reaction enthalpy

Answer 31

The measured heat change for a reaction at atmospheric pressure

Question 32

Enthalphy is state fucntion, what does this mean

Answer 32

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

Question 33

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

Answer 33

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

Question 34

What is Hess's Law

Answer 34

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.

Question 35

What is the first method for calculating Hess's Law

Answer 35

Question 36

What is the second method for using Hess's Law

Answer 36

Question 37

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

Answer 37

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

Question 38

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

Answer 38

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

Question 39

What is standard pressure

Answer 39

1 atm (atmosphere)