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Chemistry AS Level > Energerics > Flashcards

Energerics Flashcards

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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?

A

q=mcAt

17
Q

In the enthalpy change equation, what is m?

A

Mass

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
Q

In a Hess diagram, the arrows of combustion…

A

… Go down

26
Q

If the arrows of the direct route is in the opposite to the indirect route arrows, then..

A

Use the reverse sign

27
Q

In a Hess diagram, the formation arrows…

A

… Go up

28
Q

Define mean bond energy

A

Enthalpy change require to break of covalant bonds with all species in gaseous state, averages over a range of compounds

29
Q

In an exothermic reaction, the enthalpy of the system

A

Decreases

30
Q

What is the equation for the bond energy?

A

Sum of breaking-making

Chemistry AS Level (6 decks)

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