Exp 8

Question 1

What is Hess law

Answer 1

Hess law says :
All that matter is the initial and final stat of the substance not how or the pathway is entered through.

Question 2

What is this mean
Delta Hf

Answer 2

The enthalapy of formation

Question 3

What is a system ?
What is the surrounding?

Answer 3

The system is the part we are interested in
The surrounding is the part that is left around the system

Question 4

How many types of systems do we have ? What are they?

Answer 4

3
Opened system
Closed system isolated system

Question 5

In each system which transfer heat and which matter is transferred in

Answer 5

Opened transferrr both heat and matter
Closed only heat is transferred
Isolated neither heat nor matter is transferred

Question 6

There are two types of thermochemistry reactions what are they ?

Answer 6

Exothermic (release energy as heat )
Endothermic ( absorb energy as heat )

Question 7

What is the first law of thermodynamics?

Answer 7

Energy can be transferred but it can not be created or destroyed

Question 8

Describe each thermochemistry reactions in
Energy
Energy direction
q and delta H

Answer 8

Exothermic
Release energy
Energy goes from the system to the surrounding
Q=-
Delta H=-
burn reactions ( combustion reaction)

Endothermic
Absorb energy
Energy goes from the surrounding to the system
Q=+
Delta H+
(Decomposition reactions )

Question 9

What is the sign of the temperature of the surrounding?
Delta T

Answer 9

In the Exothermic delta T is positive in the surrounding
In the endothermic reaction the tempretue is negative in the surrounding.

Question 10

If the graoh shows the relation =ship between the temp and time
A) you noticed that the temp increases with time
b) you noticed that the temp decreases with time

Answer 10

A) Exothermic
b) endothermic
Remember if the graph says temp then it is talking about the surrounding not the system

Question 11

How to calculate the heat transferred between a system or two ? (q: the heat effect )

Answer 11

q = C delta T
q = c m delta T
Where
C is the heat capacity J/C
c or s is the specific heat J/C.g
m if the mas (g)
Delta T is the heat change ( t final - t initial ) C

Question 12

How is the temperature is measured?

Answer 12

Using the calorimeter

Question 13

In claorimetery what is the temperature monitored with

Answer 13

Time

Question 14

In a clorimeter graph the is the reaction Exothermic or endothermic?
A) the temperature increases with time
B) the temp decreases with time

Answer 14

A) Exothermic
B) endothermic
Note
Claorimetry measure the temp of the surrounding not the system ( it measures the heat transfer )

Question 15

What are the different types of calorimeters

Answer 15

There constant pressure calorimeter ( looks like a cup)
and the constant volume collorimeter( squeak room )

Question 16

What is a an adiabatic system in a calorimeter?

Answer 16

It is an isolated calorimeter where matter can’t flow to or from the surrounding outside the device, but could transfer from a system to another inside the calorimeter.

Question 17

In an adiabatic system what is the value of of the heat change of both the reaction and the calorimeter?

Answer 17

q rxn = - q cal

Question 18

What are the two rules of calculating the enthalpy of formation?

Answer 18

One mol of the product

Reactant should be the constituents of the compound. The physical state should be the most stable form

Question 19

What is Hess’s law

Answer 19

Change of heat is additive
Delta Hf (inthalapy of formation ) = the sum of all change in enthalpies

Question 20

In the Exothermic reaction of formation of mgo
What did we add to the mg metal?

Answer 20

Acid \ hydrocloric acid (HCl)