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UNIT 5 > CHEMISTRY- ENERGY CHANGES IN INDUSTRY > Flashcards

CHEMISTRY- ENERGY CHANGES IN INDUSTRY Flashcards

1
Q

What happens in exothermic reactions

A

Energy is released from reactants to surroundings
Temp of surroundings increases

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2
Q

What is the symbol for enthalpy change

A

Delta H

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3
Q

What happens in endothermic reactions

A

Energy takes from surroundings to reactions

Temp of surroundings decreases

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4
Q

Name diatomic elements

A

O2
H2
I2
Br2
Cl2
F2
N2

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5
Q

What is the standard enthalpy of combustion

A

Enthalpy change when 1 mole of a substance and it’s standard state burns completely in oxygen under standard conditions of 298k and one bar pressure.

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6
Q

Give an example of standard enthalpy of formation

A

H2 + 1/2 O —> H2O

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7
Q

What is the standard formation of water

A

L

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8
Q
A
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9
Q

What is the standard enthalpy of formation in their standard states

A

Zero

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10
Q

Why is the enthalpy of formation of Na zero

A

Na is an element in its standard state

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11
Q

State why the enthalpy of formation of liquid Na is not zero

A

Liquid is not sodium’s standard state

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12
Q

What is the standard enthalpy of formation

A

Enthalpy change when one mole of a substance is formed from its element under standard conditions of 298k and one bar pressure

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13
Q

What do standard enthalpies of combustion have

A

Almost always have negative values

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14
Q

Is burning a substance in oxygen exothermic or endothermic

A

Exothermic

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15
Q

What happens to substance that cannot be combusted

A

They have zero enthalpy of combustion

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16
Q

What types of substances cannot be combusted

A

Water
Carbon dioxide
And other oxides

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17
Q

Why may the enthalpy of combustion of a compound be difficult to measure

A

Incomplete combustion may occur

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18
Q

What do ions bond with

A

Water molecules

19
Q

What is the hydration of ions

A

The ions bond with water molecules
Positive ions will be attracted to the slightly negative oxygen in water molecules
Whilst negative ions will be attracted to the slightly positive hydrogens in water molecules

20
Q

What is Hess law

A

Reaction may have a very high activation energy
Reaction rate may be too slow
Possibility of competing reactions

21
Q

What is hess law used for

A

To calculate an enthalpy change indirectly

22
Q

name the type of reaction taking place when pentane burns in oxygen

A

combustion

23
Q

explain how exothermic processes affect their surroundings

A

releases heat from the system to the surroundings and the tempreture will increase

24
Q

state what is meant by the term standard enthalpy change of formation

A

when 1 mole of compound is formed from its elements under standard condition

25
Q

state what is meant by the term enthalpy change of combustion

A

when 1 mole of a substance is combusted completely in oxygen

26
Q

give one reason why the standard molar enthalpy change of formation of ethanol can not be measured directly

A

there are potentially other products and activation energy is too high

27
Q
A
28
Q

What is the definition of an enthalpy change?

A

The measure of heat given out or taken in during a process

29
Q

Why is enthalpy change used instead of energy?

A

Because we cannot easily measure energy changes

30
Q

Why is enthalpy easy to use?

A

They are measured under constant pressure
That atmosphere is at a constant pressure, so we require no extra equipment

31
Q

What type of enthalpy change does exothermic reaction have?

A

Negative

32
Q

What type of enthalpy change does endothermic reaction have?

A

Positive

33
Q

What is combustion?

A

An exothermic process that gives out heat

34
Q

What are the standard conditions for enthalpy change

A

Pressure of one bar
Temperature of 298 Kelvin
Substances in its most stable state under the above conditions

35
Q

What type of process is bond breaking?

A

Endothermic

36
Q

What type of process is bond making?

A

Exothermic

37
Q

What is the process used to extract aluminium from aluminium oxide?

A

Electrolysis

38
Q

Explain why the structure of aluminium oxide makes the compound resist to high temperature

A

Because it has a strong intermolecular forces
Has high, melting point
Contains strong electrostatic forces between the ions
Has a giant ionic structure

39
Q

What is the temperature condition for Kelvin for standard conditions

A

298

40
Q

What is the standard condition for pressure?

A

100 Kpa

41
Q

Explain why the standard enthalpy change of formation for hydrogen gas is 0 kgMol-1

A

Hydrogen gas is an element on standard conditions so no change occurs

42
Q

Name an organic compound that can be dissolved in water to manufacture hydrogen by electrolysis

A

Sodium chloride

43
Q

State one use of short chain alkanes

A

Combustion

44
Q

Explain how vanadium oxide acts as a catalyst

A

The vanadium oxide is regenerated by the end of the reaction
Vanadium oxide is oxidised by oxygen

UNIT 5 (4 decks)

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