Reactivity 1.1

Question 1

Heat

Answer 1

A form of energy (joules), measure of total energy

Question 2

Temperature

Answer 2

A measure for the average kinetic energy of the particles of a substance. Measured in degrees

Question 3

Energy changing in chemical reactions

Answer 3

No overall energy changes

Question 4

Exothermic reaction

Answer 4

Energy given out when new bonds are formed is greater than the energy required to break the bonds, excess energy is given out to the surroundings as heat

Question 5

Endothermic reaction

Answer 5

Energy given out when new bonds are formed is less than the energy required to break the bonds in the reactants, then the excess energy required is taken in from the surroundings.

Question 6

Enthalpy

Answer 6

Internal energy stored in chemical bonds (H)

Question 7

Absolute value of the enthalpy

Answer 7

This cannot be measured, but change in H can be measured during a chemical reaction at constant pressure

Question 8

H value exothermic reaction

Answer 8

Negative

Question 9

H value endothermic reaction

Answer 9

Positive

Question 10

Reaction profiles

Answer 10

Show the potential energy of the reactants and products changing during the reaction.

Question 11

Activation Energy

Answer 11

Ea, the minimum energy required for a reaction to occur

Question 12

What phase changes will be exothermic?

Answer 12

Gas to liquid, liquid to solid (where particles within the system have decreased kinetic energy and release it to the surroundings.

Question 13

What phase changes will be endothermic?

Answer 13

Solid to liquid, liquid to gas (where the system has increased kinetic energy and must absorb this from the surroundings)

Question 14

Standard Enthalpy Change Conditions

Answer 14

• Pressure of 100kPa
• Concentration of 1 mol dm-3
• All substances in their standard states
• Measured in kJ mol-1

Question 15

What is absolute temperature a measure of?

Answer 15

Measure of average kinetic energy of particles

Question 16

If the same amount of heat energy is added to two different objects made of the same material but different number of particles, what happens to the temperature?

Answer 16

The change isn’t equal due to the average kinetic energy of the particles increasing by a different amount

Question 17

Increase in temperature when an object is heated depends on… (3 factors)

Answer 17

• Mass of the object
• Heat added (Q)
• Nature of the substance

Question 18

Largest sources of error in reactions?

Answer 18

Heat loss to the surroundings

Question 19

Where does heat travel?

Answer 19

From the hotter object to the cooler object until they are in thermal equilibrium

Question 20

Exothermic reactions examples

Answer 20

Neutralisation and combustion

Question 21

Endothermic reactions examples

Answer 21

Photosynthesis and thermal decomposition

Question 22

How can you tell how stable a reactant or product is?

Answer 22

The enthalpy - the lower it is, the more stable the substance is

Question 23

Change of temperature of surroundings depends on what? (2 factors)

Answer 23

Mass of the materials making up surroundings and the specific heat capacity

Question 24

What assumption is made about dilute aqueous solutions?

Answer 24

That it has the same specific heat capacity and density as pure water.

Question 25

Calorimeter

Answer 25

Used to measure the enthalpy change in reactions occurring in solution

Question 26

Molar mass units

Answer 26

gmol^-1

Question 27

Enthalpy of solution

Answer 27

The enthalpy change when one mole of a solute is dissolved in a solvent to infinite dilution (turning a solid to aqeous ions)

Question 28

Enthalpy of formation

Answer 28

Formation of one mole of compound from its elements under standard conditions with reactants and products in their normal states

Question 29

When calculating the enthalpy change of neutralisation, what do you calculate?

Answer 29

The amount of acid neutralised