Thermochemistrty

Question 1

exothermic reaction

Answer 1

Releases energy to the surroundings, temp rise
Delta H is negative
Bonds are made

Question 2

Endothermic reaction

Answer 2

Takes in energy from the surroundings, temperature drop, delta H is positive. Bonds broken

Question 3

enthalpy change

Answer 3

Heat energy change measured under constant pressure

Question 4

enthaply

Answer 4

Heat content of a system at constant pressure

Question 5

standard conditions

Answer 5

standard states
Standard temp- 25 degrees/298K
Standard pressure- 1atm/101kPa

Question 6

Standard enthalpy change of formation

Answer 6

Empathy change when one mole of a compound is formed from its elements understand conditions and in their standard states

Question 7

Standard change of combustion

Answer 7

Enthalpy change when one mole of a substance is completely combusted with oxygen under standard conditions

Question 8

Enthalpy change of reaction

Answer 8

Enthalpy change in a reaction between the number of moles of reactants shown in the equation of a reaction under standard conditions

Question 9

Hess’s Law

Answer 9

States at the total enthalpy change for a reaction is independent of the root taken from reaction to products

Question 10

Calculating standard change of formation

Answer 10

arrows face upwards
Or
Products - reactants

Question 11

Calculating standard change of combustion

Answer 11

arrows face downwards
Or
Reactants - products

Question 12

Bond enthaply

Answer 12

The amount of energy required to break one mole of the stated bond in the gas phase

Question 13

Calorimerter diagram

Answer 13

Polystyrene cup, lid, thermometer, insulation, solution of reactants

Question 14

Spirit burner

Answer 14

clamp stand, draught shield, spirit burner, fuel, beaker, thermometer, water

Question 15

method of spirt burner

Answer 15

1. Fill beaker with 100cm3 water- initial temp with thermometer
2. Measure & record mass of spirit burner and fuel
3. light wick and heat water
   Record temp of water
   After spirit burner cools, record mass of it and remaining fuel
   Mass fuel burnt- difference

Question 16

Why results may be lower

Answer 16

• heat loss to surroundings
• incomplete combustion
• may not have been in standard conditions

Question 17

Solutions to minimise heat loss

Answer 17

• don’t place beaker too far above flame
• place lid on calorimeter
  -draught shield

Question 18

Calculating ΔH
combusion

Answer 18

1. q= mxcxΔT
   m-mass of water
   c- 4.18 Jg-3K-1
   ΔT- temp difference
2. Moles= mass/mr
   Moles= CxV/1000
3. ΔH= -q/moles

Question 19

Δh

Answer 19

products- reactants

Question 20

Exothermic enthaply profile

Answer 20

Reactants higher than products
Energy is released in bond making
Negative

Question 21

endothermic enthalpy profile

Answer 21

Products higher than reactants
More energy is required to break bonds
Positive

Question 22

Homogenous catalysts

Answer 22

Catalyst in the same phase as the reactants- take an active part in the reaction

Question 23

Heterogeneous catalysts

Answer 23

In a different phase from the reactants