Energetics

Question 1

What happens in an exothermic energy change?

Answer 1

Energy is transferred from the chemicals to the surroundings. Product have less energy than the reactants.

Question 2

Define enthalpy change

Answer 2

Amount of heat energy taken in or given out during any change in a system provided the pressure is constant

Question 3

What is △H in an exothermic reaction?

Answer 3

Negative

Question 4

Name some common oxidation exothermic processes

Answer 4

Combustion of fuels

Oxidation of carbohydrates such as glucose in respiration

Question 5

What the standard enthalpy change of a compound?

Answer 5

The enthalpy change when 1 mole of the compound is formed from its elements under standard conditions all reactants and products being in their standard state.

Question 6

What the standard enthalpy change of a compound symbol?

Answer 6

△fHθ

Question 7

What are the standard conditions for enthalpy change?

Answer 7

298K

100kPa

Question 8

What is zero degrees in K?

Answer 8

273K

Question 9

What is the standard enthalpy combustion of a substance?

Answer 9

The enthalpy change that occurs when one mole of a substance is combusted completely in oxygen under standard conditions all reactants and products being in their standard states.

Question 10

What is the standard enthalpy combustion of a substance symbol?

Answer 10

△cHθ

Question 11

What are all the standard conditions of enthalpy change?

Answer 11

100kPa
298K
Solutions at 1 mol dm-3
All substances should have their normal state at 298K

Question 12

In an endothermic reaction what happens in terms of energy?

Answer 12

Energy is transferred from the surrounding to the chemicals. They require thermal energy. Products have more energy than the reactants

Question 13

What happens to exothermic reaction in incomplete combustion?

Answer 13

Lead to soot, carbon monoxide and water. Less exothermic than complete combustion.

Question 14

Mean bond energies define

Answer 14

Mean bond energy is the enthalpy needed to break covalent bonds into gaseous atom averaged over different molecules

Question 15

State Hess’s law

Answer 15

Total enthalpy change for a reaction is independent of the route by which the chemical change takes place

Question 16

Energy change=

Answer 16

Mass of solution x heat capacity x temperature change

Question 17

What is calorimeter method?

Answer 17

Substance mixed together in closed container and the temperature rises

Question 18

What could calorimeter method be?

Answer 18

Solid dissolving or reacting in a solution or it could be two solutions reacting together

Question 19

General calorimeter method

Answer 19

Wash equipment with solution to be used 
Dry cup 
Put beaker in beaker for insulation and support
Clamp thermometer into place. Check thermometer submerged under water. 
Measure initial temperature 
Add reagent 
Stir mixture 
Measure final temperature.

Question 20

What happens if reaction is slow calorimeter?

Answer 20

Can be difficult to obtain as cooling will occur

Question 21

What do we do to combat cooling temperature?

Answer 21

Make regular time interval and extrapolated to before added to work out difference

Question 22

What do we do before we add the reagent?

Answer 22

Record results of solution without for a few minutes

Question 23

Errors in method?

Answer 23

Heat from surroundings
Approximate in specific heat capacity
Neglecting heat capacity of calorimeter
Reaction or dissolving may be incomplete or slow
Density of solution taken as same as water