5: Chemical Rx's And Stoichiometry

Question 1

Hess’s law

Answer 1

It tells us that the DH of a rx is independent of the number of steps the rx follows

Question 2

Rules of Enthalpy change when an equation is manipulated

Answer 2

• the Enthalpy change must be multiplied by the same coefficient as that of the species in the rx
• If you flip the rx, you must also change the sign
• if the rx is a sum of variable components, the Enthalpy of the rx will be the sum of the Enthalpy of the various components.

Question 3

Conditions for endothermic rx and exothermic to be spontaneous

Answer 3

• When they create too much disorder and it exceeds the energy required.
• exo: when the rx creates order, instead of disorder and it’s negative Enthalpy change exceeds the negative entropy change.

Question 4

Using DG (Gibbs free energy) to determine the spontaneity of the rx

Answer 4

DG<0, rx spo in forward direction
DG>0, rx spo in backward direction
DG=0, rx is at equilibrium