Energerics Flashcards

1
Q

In an endothermic reaction, the enthalpy of the system…

A

… Increases

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2
Q

Define enthalpy change

A

Enthalpy change is a change in (heat) energy under constant pressure

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3
Q

What is a system?

A

Reaction

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4
Q

All exothermic reactions have a positive or negative value?

A

Negative

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5
Q

All endothermic reactions have positive or negative value?

A

Positive

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6
Q

Why are endothermic reactions have a positive value?

A

The system has gained energy

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7
Q

Why do all exothermic reactions have a negative value?

A

The system gives out energy

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8
Q

What are standard conditions?

A

1 atmosphere (100,000 Pa)
1 moldm-3 (for solutions)
298K or 25C

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9
Q

What signifies standard conditions?

A

Subway sign

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10
Q

What are standard states?

A

The standard state of a substance is its most stable state under standard conditions

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11
Q

Define standard enthalpy of formation

A

Enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditions

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12
Q

What are the units for enthalpy change?

A

KJmol-1

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13
Q

In a formation reaction, what is important about the reactants?

A

They are in their element forms

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14
Q

Define standard enthalpy of combustion

A

Enthalpy change when one mole of a substance is completely burned in oxygen under standard conditions

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15
Q

What are the products of all combustion reactions?

A

CO2 and H2O

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16
Q

What is the equation for energy change?

17
Q

In the enthalpy change equation, what is m?

18
Q

In the enthalpy change equation, what is c?

A

Specific heat capacity

19
Q

In a enthalpy change equation, what is At?

A

Change in temperature

20
Q

In an exothermic reaction, the temperature…

A

… Increases

21
Q

In an endothermic reaction, the temperature…

A

… Decreases

22
Q

What is chemical system?

A

Just means the reactants and products

23
Q

What 5 things are important when drawing a enthalpy change graph?

A

Y-axis, scales, plotting, line of best fit, extrapolations

24
Q

Define Hess’ law

A

Enthalpy is independent of route taken

25
In a Hess diagram, the arrows of combustion...
... Go down
26
If the arrows of the direct route is in the opposite to the indirect route arrows, then..
Use the reverse sign
27
In a Hess diagram, the formation arrows...
... Go up
28
Define mean bond energy
Enthalpy change require to break of covalant bonds with all species in gaseous state, averages over a range of compounds
29
In an exothermic reaction, the enthalpy of the system
Decreases
30
What is the equation for the bond energy?
Sum of breaking-making