Enthalpy Change

Question 1

What is enthalpy change?

Answer 1

The amount of heat energy transferred during a chemical reaction at a constant pressure.

Question 2

units for ΔH

Answer 2

Kj mol-1

Question 3

What are the standard conditions?

Answer 3

100kPa and 298K

Question 4

Exothermic

Answer 4

gives out energy

ΔH is negative

Question 5

Give an example of exothermic reaction:

Answer 5

1. combustion of methane

Question 6

Endothermic reactions

Answer 6

Absorb energy
ΔH is positive

Question 7

What reaction is bond breaking?

Answer 7

endothermic- you need energy to break bonds

Question 8

What reaction is once the bonds are formed?

Answer 8

Exothermic as energy is released.

Question 9

What is bond enthalpy?

Answer 9

Bond enthalpy is the energy required to break bonds.

Question 10

Define standard enthalpy of formation

Answer 10

the enthalpy change when 1 mole of a compound is formed from its elements in their standard state under standard conditions.

Question 11

Define standard enthalpy of combustion.

Answer 11

the enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions.

Question 12

Define specific heat capacity

Answer 12

The amount of energy required to raise the temperature of 1g by 1k.

Question 13

If the surroundings have a lower specific heat capacity what happened

Answer 13

An exothermic reaction will cause a bigger increase in the temperature of the surroundings

Question 14

What are the units for specific heat capacity

Answer 14

Jk-1g-1

Question 15

Equation for enthalpy change

Answer 15

Q= mcAt

Q- amount of heat energy given out or taken in (J)
M- mass of the surrounding (g)
c- specific heat capacity

Question 16

If the reaction is exothermic

Answer 16

We add a negative sign at the front

Question 17

If the reaction is endothermic

Answer 17

Add a + sign to the front

Question 18

Simple flame calorimetry

Answer 18

Burn water using a flame.
Measure the temperature change of the water

Question 19

What are some problems with the simple flame calorimeter

Answer 19

Some of the energy will be lost.e.g the water will give off vapours into the air.
To prevent this, increase the mass of the water but this can cause such a small change in temperature.

Question 20

How do you find the molar enthalpy?

Answer 20

Divide the enthalpy change by the moles

Question 21

What element are found as gases under standard state?

Answer 21

Nitrogen
oxygen
chlorine
fluorine
hydrogen
And all noble gases

Question 22

What elements are found as liquid under their standard state?

Answer 22

Bromine and mercury

Question 23

If an element is under standard state what is their enthalpy change?

Answer 23

Always zero!

Question 24

When a metal reacts with oxygen, what will it form?

Answer 24

Metal+ oxgyen——> metal oxide

Question 25

Define enthalpy of combustion

Answer 25

The standard enthalpy of combustion is when one mole of a substance is fully burned in oxygen under standard conditions with all reactants and products under their standard state

Question 26

Define Hess’s law

Answer 26

The enthalpy change in a reaction at constant pressure is independent of the route taken

Question 27

Arrows for enthalpy of formation

Answer 27

The both face upwards so arrow one needs to be flipped

Question 28

How is an exothermic reaction shown from a thermometer?

Answer 28

A rise in temperature

Question 29

How is a endothermic reaction shown by a thermometer?

Answer 29

Temperature drops