Unit 6 Energetics

Question 1

What are the standard conditions for the standard enthalpy change?

Answer 1

Pressure - 100kPa

Temperature - 298K

Question 2

What are the types of standard enthalpy change reactions and provide a brief explanation

Answer 2

Exothermic - releases energy in the form of heat
A+B->C+D+heat

Endothermic - absorbs energy
A+B+heat->C+D

Question 3

What is the average bond enthalpy formula?

Answer 3

ΔHreaction = ΔHreactants - ΔHproducts

Question 4

What is the specific heat capacity of water?

Answer 4

4.18 Jg-1K-1

Question 5

What is the formula for enthalpy change in water?

And what do each letter symbolize?

Answer 5

Energy change = mc ΔT

c - specific heat constant
m - mass
ΔT - change in temperature

Question 6

What are the rules for energy change?

Answer 6

Net change in energy is zero

0 = energy lost + energy gained

And the final temperature (Tfinal) for energy change will be the same for all substances

Question 7

Define enthalpy of reaction

Answer 7

the measure of heat energy transferred for a chemical reaction

Question 8

What is the formula to determine ΔT?

Answer 8

ΔT = Texprapolated - Tinital

Question 9

What is the specific heat constant for steam and how do you determine the energy change?

Answer 9

energy change = mcΔT

c = 2.02 Jg^-1 K^-1

Question 10

How do you determine the change in energy for steam condensing into water and what is the value for enthalpy of vapourization?

Answer 10

energy change = enthalpy of vapourization X mass

ΔH = 2260 J/g or 40.7 kJ/mol

Question 11

What is the specific heat constant for water and how do you find the change in energy?

Answer 11

energy change = mcΔT

c = 4.18 Jg^-1 K^-1

Question 12

What is the value for the enthalpy of fusion and how do you determine the energy change for water freezing to ice?

Answer 12

energy change = enthalpy of fussion X mass

ΔH = 334 J/g or 6.02 kJ/mol

Question 13

What is the specific heat constant for ice and how do you determine change in energy?

Answer 13

energy change = mcΔT

c = 2.06 Jg^-1 K^-1

Question 14

What is Hess’s Law state?

Answer 14

The enthalpy change of a reaction depends only on difference between reactant and products

Question 15

How do you apply Hess’s Law to determine ΔH of reaction?

Answer 15

1) Write out the overall chemical reaction for ΔH reaction wanted
2) Identify the reaction where ΔH reaction is known
3) Manipulate each reaction and its ΔH reaction by:
a) reversing products and reactants
b) multiplying reaction by a value of “x”
4) Cancel substances occurring on both products and reactants sides paying attention to states and coefficients
5) Confirm that non-cancelled substances add up to desired reaction
6) Add up all the new ΔH for the reaction