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Chemistry > DF > Flashcards

DF Flashcards

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1
Q

What is thermochemistry?

A

The study of the energy and heat associated with chemical reactions

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2
Q

Fuels can only release energy once _______

A

Combined with oxygen

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3
Q

Define exothermic reaction

A

A reaction that gives out energy and heats the surroundings
Has a negative enthalpy change/ ^H

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4
Q

Define endothermic reaction

A

A reaction that takes in energy and cools the surroundings
Has a positive enthalpy change/ ^H

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5
Q

What is enthalpy change?

A

The quantity of energy transferred in a reaction, shown by ^H and measured in KJmol-1

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6
Q

What is an enthalpy diagram?

A

A diagram showing the change in energy from a line representing the reactants to a line representing the products

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7
Q

True or false you can measure enthalpy?

A

False, you can only measure the change in enthalpy

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8
Q

What is the equation to find the change in enthalpy?

A

^H = H(products) - H(reactants)
^ represents delta (change)

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9
Q

What is ‘the system’?

A

The reactants and the products of the reaction that the chemists are interested in
May lose or gain enthalpy as a result of the reaction

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10
Q

What does ‘the surroundings’ refer to?

A

The rest of the world that is not concerned on the reaction

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11
Q

What are the standard conditions?

A
  • specified temperature, (298K, 25°c)
  • standard pressure of 1 atm
  • standard concentration of 1moldm-3 for solutions
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12
Q

Define standard states

A

The physical state of a substance under standard conditions

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13
Q

What is Kelvin?

A

Kelvin, K is the SI (international system) unit that could always be used in calculations
0K is known as absolute zero
To convert between kelvin and Celsius +273

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14
Q

What is the standard enthalpy change for a reaction?

A

The enthalpy change when molar quantities of reactants as stated in their equation react together under standard conditions

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15
Q

By measuring _______ change you can calculate _______ change

A

Temperature, enthalpy

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16
Q

What is the equation for energy transferred?

A

Energy transferred,q,J = specific heat capacity, C,Jg-1K-1 x mass,m,g x temp.change,^T,K

17
Q

What is standard enthalpy change of combustion?

A

The enthalpy change that occurs when one mole of a substance is burnt completely in oxygen under standard conditions in standard states
The ^H is always negative

18
Q

How do you calculate SEC of combustion in practice?

A

In practice it is often impossible to measure so adjustments are made after to allow for the non-standard conditions

19
Q

What is the standard enthalpy change of formation?

A

The enthalpy change that occurs when one mole of a compound is formed from its elements under the standard conditions in standard states
The SEC of formation of a pure element in its standard state is 0

20
Q

How can SEC of formation be calculated?

A

By making use of known quantities and incorporating these into an enthalpy cycle

21
Q

What is the standard enthalpy change of neutralisation?

A

The enthalpy change when one mole of hydrogen ions react with one mole of hydroxide ions to form one mole of water under standard conditions

22
Q

What equation can be used to show SEC of neutralisation?

A

H+ + OH- —> H2O

23
Q

When writing equations for SEC what must be done?

A

The equation must always be balances to show one mole of the substance reacting, even if this mean halving a mole of oxygen

24
Q

What is an enthalpy cycle?

A

A way of working out an enthalpy change either directly or indirectly

25
Q

What is Hess’ law?

A

States the enthalpy change for any chemical reaction is independent of the intermediate stages, so long as initial and final conditions are the same for each route

26
Q

The total enthalpy change for the indirect route __________ the enthalpy via the direct route

A

As same as

27
Q

What are more important, reaction profiles or energy level diagrams?

A

Reaction profiles as they show activation energy

28
Q

Define activation energy

A

The minimum amount of energy needed to react

29
Q

What is complete combustion?

A

Occurs when there is a good supply of oxygen, releasing the maximum amount of energy

30
Q

What is incomplete combustion?

A

Occurs when there is a bad supply of oxygen, less energy is released

31
Q

What problems can incomplete combustion cause?

A
  • carbon monoxide is poisonous
  • particular carbon causes respiration problems and global dimming
32
Q

Define Enthalpy, H

A

The energy content stored in a chemical system

33
Q

1K in temperature change = _ °c

A

1

Chemistry (4 decks)

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