Hess's Law

Question 1

What does Hess’s law state?

Answer 1

The enthalpy change for a chemical reaction is the same, whatever route is taken from reactants to products essentially the law of Conservation of Energy

onlu depends on initial and final states

Question 2

What is the enthalpy of formation?

Answer 2

The enthalpy change when one mole compoud is formed from its constituent elements under stndard conditons, all reactants and products being in their standard states

Question 3

What is the equation for Hess’s law?

Answer 3

Question 4

What is the difference when using a thermochemical cycles using enthalpy changes of combustion?

Answer 4

reactants often do not react directly to form the compound we are interested in

Question 5

What is the enthalpy change of combustion?

Answer 5

• Δ_CH^θ​
• enthalpy change when one mole of a substance is completely burnt in oxygen under standard conditions

Question 6

How do you work out the enthalpy of combustion, using the enthalpy of combustion data?

Answer 6

where the intermediates are the products of combustion

Question 7

How enthalpy of formation be worked out from enthalpy of combustion>

Answer 7

• if all products will readily burn
• can be put into an ethalpy of combustion cycle