Energetics

Question 1

What is a limiting reagent?

Answer 1

a reactant that runs out first AND decides the amount of products.

Question 2

Endothermic reactions have…

Answer 2

Positive enthalpy charge

Question 3

Exothermic reactions have…

Answer 3

Negative enthalpy charge

Question 4

What are the standard conditions for reactions?

Answer 4

100kPa
298K

Question 5

Define mean bond enthalpy

Answer 5

THE ENTHALPY CHANGE WHEN ONE MOLE of covalent bonds are broken, averaged over a range of compounds. (always a positive value).

Question 6

Define standard enthalpy change of reaction.

Answer 6

THE ENTHALPY CHANGE WHEN a reaction occurs in the molar quantities shown in the balanced chemical equation under standard conditions.

Question 7

Define standard enthalpy change of formation.

Answer 7

THE ENTHALPY CHANGE WHEN ONE MOLE OF a substance is formed from its elements with reactants and products in their standard states under standard conditions.

Question 8

Define standard enthalpy change of combustion.

Answer 8

THE ENTHALPY CHANGE WHEN ONE MOLE OF substance is completely burnt in oxygen under standard conditions in standard states.

Question 9

q=mc^T

Answer 9

q= energy transferred (to the substance changing temp) (J)
m= mass of the substance (changing temp) (g)
c= specific heat capacity (of substance changing temp)
^T= change in temp
,

Question 10

Define Hess’ Law.

Answer 10

The total enthalpy change for a chemical reaction is independent of the route taken.

Question 11

^rH equation

Answer 11

^rH = (the sum of the bond enthalpy of reactants) - (the sum of the bond enthalpies in products)