General definitions

Question 1

Define biofuel.

Answer 1

• a fuel derived from organic or living matter

Question 2

Define carbon-neutral.

Answer 2

An activity that has no net carbon emissions to the atmosphere

Question 3

Define the terms addition and elimination.

Answer 3

Addition: a chemical reaction in which two molecules form a larger molecule, or one which increases the number of substituents on a molecule
Elimination: a reaction in which a simple molecule is removed from a larger molecule

Question 4

Define electronegativity.

Answer 4

The power/tendency of an atom to attract the pair of electrons in a covalent bond

Question 5

Define enthalpy of formation.

Answer 5

• The enthalpy change when 1 mole of a substance is formed from it’s constituent elements, with all reactants and products in their standard states at standard pressure

Question 6

Explain, in general terms, how a catalyst works.

Answer 6

• a catalyst provides an alternative route which has a lower activation energy.

Question 7

Define enthalpy of combustion.

Answer 7

-The enthalpy change when 1 mole of a substance is burned completely in excess oxygen, with all reactants and products in their standard states, under standard pressure

Question 8

Define Hess’s Law.

Answer 8

-The enthalpy change of a reaction is independent of the route taken, and only depends on the initial and final states.

Question 9

Define enthalpy

Answer 9

• Heat change at constant pressure.

Question 10

Define activation energy.

Answer 10

• The minimum energy particles require for a reaction to occur.

Question 11

Suggest all 5 reasons why the enthalpy of combustion from an experiment may not be that in a databook.

Answer 11

-not standard conditions
-evaporation of water/fuel
-heat loss to surroundings
-incomplete combustion
-heat transferred to container

Question 12

In an experiment to obtain the enthalpy of combustion of a hydrocarbon, the value a student obtains is much less than the value in a databook. Give as many possible ways the experimental apparatus/method could be improved.

Answer 12

-Use a lid
-insulate the container
-use a wind shield

Question 13

In a determination of the standard enthalpy change of an exothermic reaction, a student measures the initial and final temperature to determine the temperature change. Suggest a new, improved method, and explain your answer.

Answer 13

• measure and record T for a few minutes before starting, take a mean to determine initial temperature
• measure and record T every minute after adding reactants, until reaction is finished
• plot a graph of T against time, draw a line of best fit and extrapolate back to starting point to determine a more accurate value for the temperature change that accounts for cooling