Module 3: Enthalpy changes

Question 1

What’s the definition of enthalpy change?

Answer 1

The amount of heat energy transferred during a chemical reaction at a constant pressure.

Question 2

Draw an exothermic reaction

Answer 2

• Reactants above products. Delta H = negative

Question 3

Draw an endothermic reaction

Answer 3

• Reactants below products. Delta H is positive =.

Question 4

What’s activation energy?

Answer 4

The minimum energy required for a reaction to take place by breaking bonds.

Question 5

Define standard enthalpy change of a reaction

Answer 5

The enthalpy change for a given reaction in the molar quantities shown in the equation.

Question 6

What’s standard enthalpy change of combustion?

Answer 6

The enthalpy change when 1 mol of a substance completely combusts at 298k and 100Kpa. ALWAYS EXOTHERMIC

Question 7

What’s the standard enthalpy of combustion?

Answer 7

The enthalpy change when 1 mol of a compound is formed from its elements at 298 K and 100Kpa. CAN BE EITHER ENDO OR EXO.

Question 8

What’s standard enthalpy change of neutralisation?

Answer 8

The enthalpy change when 1 mol of H2O is formed from a reaction of H+ and OH- at 298K and 100Kpa. ALWAYS EXOTHERMIC (at approx -57 kJ mol). Always measured per mol of H2O formed.

Question 9

Why do we use calorimetry?

Answer 9

We can measure the temp change of water.

Question 10

What’s the equation for Energy change?

Answer 10

Q = MC(delta)T

q = energy change in joules
m = mass of water (solution) in grams
c = specific heat capacity in 1 gram per kelvin.
t = change in temp of solution (Celsius/Kelvin)

Question 11

What’s the equation for enthalpy change?

Answer 11

q x 10-3 /n

Question 12

What’s the apparatus for the calorimetry combustion reaction?

Answer 12

1. Clamp stand
2. Copper container attached to clampn stand with water in
3. Thermometer in water
4. Spirit burner

Question 13

What’s the apparatus for a reaction in a solution?

Answer 13

1. Beaker
2. Styrofoam cup in beaker.
3. Reactants
4. Stirrer —–> Products.
5. Solvent.

Question 14

What acts as the surroundings and the chemical system in the combustion experiment?

Answer 14

Water and the fuel burning.

Question 15

What acts as the surroundings and the chemical system in the reaction with a solution calorimetry experiment?

Answer 15

The solution and the chemical reacting/dissolving.

Question 16

What do we use when calculating moles?

Answer 16

The limiting reagent.