1. enthalpy changes

Question 1

Enthalpy change delta H

Answer 1

is the heat energy transferred in a reaction at constant pressure

Question 2

what are the units of enthalpy change (delta H)

Answer 2

kJmol-1

Question 3

delta H theta means

Answer 3

measurements made under standard conditions and elements were in their standard states

Question 4

what are standard conditions

Answer 4

100 kPa

298 K

Question 5

exothermic reactions

1. what do they do concerning energy
2. is delta H + or -

Answer 5

1. give out energy

2. negative

Question 6

exothermic

1. what reaction is usually exothermic
2. examples

Answer 6

1. oxidation
2. combustion of a fuel like methane.
   CH4(g) + 2O2(g) -> CO2(g) + 2H2O(l)
   oxidation of carbs such as glucose in respiration
   C6H12O6

Question 7

endothermic reactions

1. what do they do concerning energy
2. is delta H + or -

Answer 7

1. absorb energy

2. positive

Question 8

endothermic

2 e.g. of endothermic reaction

Answer 8

1. thermal decoposition of calcium carbonate
   CaCO3(s) -> CaO(s) + CO2(g)
2. main reactions of photosynthesis (sunlight supplies energy

Question 9

what do enthalpy profile diagrams show

Answer 9

how enthalpy (energy) changes during reactions

Question 10

what is the activation energy Ea

Answer 10

the minimum amount of energy needed to begin breaking reactants bonds and start a chemical reaction

Question 11

2 ways of finding enthalpy change

Answer 11

experiment

data books

Question 12

enthalpy are affected by _____

so it is important to measure enthalpy under _____

Answer 12

temperature and pressure

standard conditions

Question 13

definition

standard enthalpy change of reaction (delta r H theta)

Answer 13

enthalpy change
when the reaction occurs in the molar quantities
shown in the chemical equation
under standard conditions

Question 14

definition

standard enthalpy change of formation (delta f H theta)

Answer 14

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

Question 15

definition

standard enthalpy change of combustion (delta c H theta)

Answer 15

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

Question 16

definition

standard enthalpy change of neutralisation (delta neut H theta)

Answer 16

enthalpy change
when an acid and an alkali react together
under standard conditions
to form 1 mole of water