Energetics - defination

Question 1

Define enthalpy change

Answer 1

Change in heat energy at constant pressure

Question 2

What is the symbol for enthalpy change?

Answer 2

ΔH

Question 3

What are the units for enthalpy change?

Answer 3

kJ mol−1

Question 4

What happens in an exothermic process?

Answer 4

Energy is released to the surroundings

Question 5

How does the temperature of the surroundings change during an exothermic process?

Answer 5

The temperature of the surroundings increases

Question 6

What is the sign of the enthalpy change in an exothermic reaction?

Answer 6

Negative

Question 7

What happens in an endothermic process?

Answer 7

Energy is taken in from the surroundings

Question 8

How does the temperature of the surroundings change during an endothermic process?

Answer 8

The temperature of the surroundings decreases

Question 9

What is the sign of the enthalpy change in an endothermic reaction?

Answer 9

Positive

Question 10

What type of processes have a negative enthalpy change?

Answer 10

Exothermic

Question 11

What type of processes have a positive enthalpy change?

Answer 11

Endothermic

Question 12

What are standard conditions?

Answer 12

100 kPa pressure, 298 K temperature, 1.0 mol dm−3 concentration for all solutions

Question 13

What is the standard state of a substance?

Answer 13

Its state (solid, liquid, gas) under standard conditions

Question 14

What symbol is given to enthalpy changes measured under standard conditions?

Answer 14

ΔH^θ

Question 15

Is breaking bonds an exothermic or endothermic process?

Answer 15

Endothermic

Question 16

Is making bonds an exothermic or endothermic process?

Answer 16

Exothermic

Question 17

What is acitvation energy?

Answer 17

The minimum needed energy to start a reaction

Question 18

What is the symbol for activation energy?

Answer 18

Ea

Question 19

Define mean bond enthalpy

Answer 19

The energy required to break one mole of a covalent bond into gaseous atoms, averaged over a range of different compounds

Question 20

What sign do mean bond enthalpies always have?

Answer 20

Positive

Question 21

Why are all bond enthalpies positive?

Answer 21

An input of energy is needed to break a bond (endothermic process)

Question 22

Define standard enthalpy of formation

Answer 22

The enthalpy change when one mole of substance is formed from its constituent elements under standard conditions with all reactants and products being in their standard states

Question 23

What is the standard enthalpy of formation for an element in its standard state?

Answer 23

Zero

Question 24

When does an element have a standard enthalpy of formation that isn’t zero

Answer 24

When the element is not in its standard state

Question 25

Define standard enthalpy of combustion

Answer 25

The enthalpy change when one mole of a substance is completely burnt in excess oxygen under standard conditions,with all reactants and products being in their standard states