4. Energetics Flashcards Preview

AQA A Level Physical Chemistry > 4. Energetics > Flashcards

Flashcards in 4. Energetics Deck (91)
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1

What is energy transfer during a reaction due to?

The breaking and forming of bonds

2

What happens to energy when bonds are broken?

Energy is taken in

3

What happens to energy when bonds are formed?

Energy is released

4

In terms of bonds, when is energy taken in?

When bonds are broken

5

In terms of bonds, when is energy released?

When bonds are formed

6

What is stored energy known as?

Enthalpy

7

What is the symbol for enthalpy?

H

8

What is enthalpy?

Stored energy

9

Can enthalpy be measured?

No

10

How can enthalpy changes be found?

By measuring the change in temperature during reactions - at a constant pressure

11

What must be constant when measuring change in temperature to work out enthalpy change?

Pressure

12

What is the mnemonic to remember energy when breaking/making bonds?

Bendy Mexicans

(breaking = endo, making = exo)

13

What happens to energy in an endothermic reaction?

It is taken in

14

When energy is taken in during an endothermic reaction, what form does it usually take?

Heat

15

What happens to the temperature of the surroundings during an endothermic reaction?

It decreases

16

What is higher in an endothermic reaction; the energy to make bonds or to break them?

Energy to break bonds is higher than to make them

17

What does it mean, in terms of energy, that endothermic reactions need more energy to break bonds than to make them?

There is an overall need for energy for the reaction to take place = positive ΔH value

18

Why do endothermic reactions have a positive ΔH value?

There is an overall need for energy in order for the reaction to take place - so the system gains energy

19

Do endothermic reactions have a positive or negative ΔH value?

Positive

20

What happens to energy in an exothermic reaction?

It is released

21

When energy is released during an endothermic reaction, what form does it usually take?

Heat

22

What happens to the temperature of the surroundings during an exothermic reaction?

It increases

23

Why does the temperature of the surroundings increase during an exothermic reaction?

Energy is transferred to the surroundings

24

What is higher in an exothermic reaction; the energy to make bonds or to break them?

The energy when making bonds

25

What does it mean, in terms of energy, that exothermic reactions need less energy to break bonds than to make them?

There is an overall release of energy when the reaction takes place = negative ΔH value

26

Why do exothermic reactions have a negative ΔH value?

There is an overall release of energy when a reaction takes place - so the system loses energy

27

Does a system lose or gain energy during an endothermic reaction?

Gains energy

28

Does a system lose or gain energy during an exothermic reaction?

Loses energy

29

What do values for enthalpy change depend on?

The pressure and temperature at which the reaction is carried out at

30

What is the standard enthalpy change of a reaction?

The heat energy exchange with its surroundings at a constant pressure and temperature (under standard conditions)