Enthalpy changes (9.1)

Question 1

What is enthalpy?

Answer 1

A measure of heat energy in an atom, ion or chemical system.

Question 2

What does H stand for?

Answer 2

Enthalpy

Question 3

Can enthalpy itself be measured?

Answer 3

No, only enthalpy changes can.

Question 4

What is the general equation for enthalpy changes?

Answer 4

Enthalpy change = products - reactants

Question 5

If an enthalpy change is negative what kind of reaction took place?

Answer 5

Exothermic

Question 6

If an enthalpy change is positive what kind of reaction took place?

Answer 6

Endothermic

Question 7

What is heat energy transferred to when enthalpy of a product changes?

Answer 7

-The system (reactant or product)
-The surroundings

Question 8

What is activation energy?

Answer 8

The minimum amount of energy needed for a reaction to occur.

Question 9

What kind of activation energy makes a reaction rapid?

Answer 9

A smaller activation energy due to the energy needed already being readily available.

Question 10

Enthalpy changes can differ depending on conditions. How do chemists combat this?

Answer 10

Using standard conditions

Question 11

What is enthalpy change’s units usually?

Answer 11

kjmol-1

Question 12

What is the standard pressure?

Answer 12

101 kPa

Question 13

What is standard temperature?

Answer 13

298K / 25 degrees Celsius

Question 14

What is standard concentration?

Answer 14

1 mol dm-3

Question 15

Do balancing numbers affect enthalpy changes?

Answer 15

Yes