Thermochemistry

Question 1

When is the Q=mcT equation used?

Answer 1

Q-mcT us used to calculate heat transferred in a process where there is no phase change

Question 2

Where is a vast majority of all the energy within Earth’s biosphere derived from?

Answer 2

Solar energy

Question 3

How does the sun produce energy?

Answer 3

Hydrogen atoms aret converted into helium atoms in a highly exothermic nuclear fusion reaction

Question 4

How do plants and animals store chemical energy?

Answer 4

In the molecular bonds of a number of organic compounds such as starches, sugars, and carbohydrates.

Question 5

What does thermal energy refer to?

Answer 5

The TOTAL kinetic energy of the molecules

Question 6

What happens to energy when a bonds form and break?

Answer 6

Bonds breaking: Energy required
Bonds forming: Energy released

Question 7

Chemical reactions will have a change in energy because of the energy changes that occur when __________________.

Answer 7

old bonds are broken and new bond form

Question 8

What is temperature?

Answer 8

The AVERAGE kinetic energy of the molecules in the sample

Question 9

What is heat?

Answer 9

the transfer of kinetic energy from one object to another

Question 10

What is enthalpy?

Answer 10

The change in potential energy between the reactants and products at a constant pressure. It is equal to the heat absorbed or released by the system.

Question 11

What is molar enthalpy?

Answer 11

Molar enthalpy is the enthalpy per mole of a specified substance in the reaction equation.

Question 12

Will exothermic and endothermic reactions have positive or negative enthalpies?

Answer 12

Endothermic: positive
Exothermic: Negative

Question 13

If the coefficients of the reaction change, the enthalpies of the reaction change _________.

Answer 13

by the same factor

Question 14

Photosynthesis is an __________(1) process. Cellular respiration is an ______________(2) process. Hydrocarbon combustion is an _____________(3) process.

Answer 14

(1) Endothermic
(2) Exothermic
(3) Exothermic

Question 15

What is an activated complex?

Answer 15

The activated complex is an unstable intermediate in a transition state between reactants and products. The peak of the energy diagram

Question 16

When more bond are being formed than broken, an _________ reaction is occurring.

Answer 16

exothermic

Question 17

When more bonds are being broken than formed, an _________ reaction is occurring.

Answer 17

endothermic

Question 18

What is collision theory?

Answer 18

To react, molecules must collide with the correct orientation and enough energy to overcome the activation energy barrier.

Question 19

In an ___________ reaction, the products contain more potential energy in their bonds than the reactants

Answer 19

endothermic

Question 20

In an __________ reaction, the products contain less potential energy in their bonds than the reactants.

Answer 20

exothermic

Question 21

What is a catalyst?

Answer 21

Catalysts cause the rates of reactions to increase. They do NOT affect the value of the enthalpy change.

Catalysts lower the activation energy by changing the reaction pathway. They lower both the reverse and forward activation energy. They also increase the probability of successful collisions.

Question 22

What are the 4 ways to increase the rate of reaction?

Answer 22

1. Increase temperature
2. Increase pressure
3. Increase concentration
4. Add a catalyst

Question 23

How does increasing the temperature cause an increase in the rate of a reaction?

Answer 23

The number of collisions increases and the energies of the collisions have more energy to overcome the activation energy

Question 24

Does a change in temperature affect endothermic or exothermic reactions more?

Answer 24

Since endothermic reactions require a greater amount of activation energy, an increase in temperature affects endothermic reactions more than exothermic reactions

Question 25

How does increasing the pressure of gases increase the rate of reaction?

Answer 25

Reducing the volume results in an increase in the rate of reaction by increasing the number of reactions(doesn't change orientation or activation energy) ONLY AFFECTS GASES IN A REACTION!!

Question 26

What impact does adding an inert gas have on the rate of reaction?

Answer 26

An inert gas is a non-reactive gas so it has no effect on rate of reaction.

Question 27

How does increasing concentration increase the rate of reaction?

Answer 27

Adding more reactant into the bottle leads to more molecules causing more collisions.

Question 28

What is the first law of thermodynamics?

Answer 28

Energy can not be created or destroyed, only transformed

Question 29

If a reactions potential energy energy increases, the surrounding kinetic energy __________(1). If a reactions potential energy ___________(2), the surrounding kinetic increases.

Answer 29

(1) decreases (2) decreases

Question 30

What does a system refer to?

Answer 30

- The tiny bit of matter that is being studied - Can be a specific reactant/product/reaction

Question 31

What is an open system?

Answer 31

Matter and energy can transfer, like a can of pop

Question 32

What is a closed system?

Answer 32

Only energy can move, matter can not, like a closed can of pop

Question 33

What is an isolated system?

Answer 33

No matter and no energy is transferred In chemistry, we assume that systems are isolated, although this is actually impossible to fully achieve

Question 34

What type of system is a beaker of liquid?

Answer 34

- Over a short period of time, a beaker of liquid can act like a closed system(matter lost is insignificant) - Over a long period of time, it be comes an open system

Question 35

What do surroundings refer to?

Answer 35

Everything in the universe that is not the system

Question 36

An endothermic reaction feels ______(1) as energy is __________________(2) and going into the ________________(3) of the reaction. The change in the chemical potential of the reaction is ______________(4).

Answer 36

(1) cold (2) being taken from the surroundings (3) chemical potential energy (4) postive/increasing

Question 37

An exothermic reaction feels ______(1) as thermal energy is __________________(2). The change in the chemical potential of the reaction is ______________(3).

Answer 37

(1) hot (2) transferred to the surroundings (3) negative/decreases

Question 38

What is calorimetry?

Answer 38

The process of measuring heat change in a chemical reaction

Question 39

What is an assumption with calorimetry?

Answer 39

The system is isolated

Question 40

How do you calculate percent efficiency?

Answer 40

(experimental)/(theoretical) x 100%

Question 41

How do you calculate molar enthalpy?

Answer 41

(delta)H = -Q(cal)/n(limiting)

Question 42

The amount of ____________(1) the water gained or lost is ___________________(2) to the amount of energy the reaction ______________(3).

Answer 42

(1)energy(heat) (2) equal and opposite (3) gained/lost (delta)kinetic energy of water = -(delta)H run

Question 43

In the formula Q=mcT, mass is measured in _________(1).

Answer 43

grams

Question 44

What is specific heat capacity?

Answer 44

How much energy it takes to heat 1g of substance to increase by 1 degree celsius.

Question 45

If the calorimeter is not made of ____________(1), it's heat should __________(2).

Answer 45

(1) polystyrene (2) not be ignored

Question 46

What are the four different ways to communicate enthalpy changes?

Answer 46

1. As molar enthalpy 2. As a (delta)H term at the end of a balanced reaction 3. Write it as an energy term in the balanced reaction (reactant if endothermic, product if exothermic) 4. As a potential energy diagram

Question 47

What does the potential energy diagram look like for an endothermic reaction?

Answer 47

up to down

Question 48

What does the potential energy diagram look like for an exothermic reaction?

Answer 48

up to down

Question 49

What are the labels on the x and y axis for a potential energy diagram?

Answer 49

x axis: reaction coordinate(no units) y axis: potential energy(kJ)

Question 50

What is modified Hess' Law?

Answer 50

Refer to notebook

Question 51

While increasing the pressure of gases in a system leads to more collisions with the correct orientation, it doesn't actually change the ____________ of collisions.

Answer 51

proportion

Question 52

In comparison to exothermic reactions, endothermic reactions require ___________(1) to create an activated complex.

Answer 52

(1) more kinetic energy