5.2 ENERGETICS

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Total cards: 24•Content version: v4•Public deck•Updated: 8/1/2026

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Front (Question)

Define an enthalpy change of a reaction

Back (Answer)

The heat energy it releases or absorbs per mole

Front (Question)

Is heat energy absorbed or released in an ENDOthermic reaction (and so what enthalphy sign is it)

Back (Answer)

Absorbed (+)

Front (Question)

Is heat energy absorbed or released in an EXOthermic reaction (and so what enthalphy sign is it)

Back (Answer)

Released (-)

Front (Question)

Units of enthalpy

Back (Answer)

kJ/mol

Front (Question)

How do you draw an energy level diagram for an ENDOthermic reaction

Back (Answer)

• Enthalpy scale on y-axis, and time/progression on x-axis • Reactants drawn on line on bottom of diagram • Vertical line up with an arrow (labelled with enthalpy) • Products of horizontal line above line

Front (Question)

How do you draw an energy level diagram for an EXOthermic reaction

Back (Answer)

• Enthalpy scale on y-axis, and time/progression on x-axis • Reactants drawn on line at top of diagram • Vertical line down with an arrow (labelled with enthalpy) • Products of horizontal line below

Front (Question)

When bonds are broken, what type of reaction is it

Back (Answer)

Endothermic

Front (Question)

When bonds are broken, what type of reaction is it

Back (Answer)

Endothermic - energy is absorbed

Front (Question)

When bonds are made, what type of reaction is it

Back (Answer)

Exothermic - energy is released

#10

Front (Question)

Unit for bond energy

Back (Answer)

kJ/mol

#11

Front (Question)

Equation for calculating with bond energies

Back (Answer)

Enthalpy change = Bonds broken - bonds made

#12

Front (Question)

How to calculate a bond energy question

Back (Answer)

• Add up each individual bond energy for each bond • Add them together for products and reactants • Subtract products from reactants

#13

Front (Question)

In an exothermic reaction, what is the ‘ratio’ of energy absorbed / released

Back (Answer)

Released > Absorbed

#14

Front (Question)

In an exothermic reaction, what is the ‘ratio’ of energy absorbed / released

Back (Answer)

Released > Absorbed

#15

Front (Question)

In an endothermic reaction, what is the ‘ratio’ of energy absorbed/released

Back (Answer)

Absorbed > Released

#16

Front (Question)

In an endothermic reaction, what is the ‘ratio’ of energy absorbed/released

Back (Answer)

Absorbed > Released

#17

Front (Question)

What is the activation energy

Back (Answer)

The energy needed to break the bonds

#18

Front (Question)

How do you make an energy level diagram, a reaction profile diagram

Back (Answer)

• There is a hump from the products to the reactants • In the centre of the hump, and arrow up • Labelled activation energy and the actual enthalpy (if avaliable)

#19

Front (Question)

Q =

Back (Answer)

Q=mc 0t

#20

Front (Question)

Enthalpy Change equation

Back (Answer)

-Q / moles

#21

Front (Question)

Describe how to carry out a combustion calorimetry experiment

Back (Answer)

• Weigh 50g of water and plae in a can above a burner • Measure inital mass of burner and intital temperature of water • Ignite the burner, stir water for 30s then extinguish burner • Measure final mass of burner, and final temperature of water

#22

Front (Question)

How to calculate enthalpy change from a combustion calorimetry experiment

Back (Answer)

• Q=mc0t (of water) • CONVERT TO KJ • Moles of fuel • Enthalpy = -Q/moles

#23

Front (Question)

What are the main sources of error in a combustion calorimetry experiment

Back (Answer)

• Heat loss - most of the thermal energy heats the air • Incomplete combustion - releases less heat energy

#24

Front (Question)

How do endothermic reactions get given a ‘+’ value for enthalpy change when being calculated

Back (Answer)

Q=mc0t will be negative and so -Q/mol (negative multipied by negative) will be positive