Chapter 10: Energy

For each picture:

* draw an arrow showing direction of heat flow

* label –q and +q

Lesson 1 – Heat

Heat (____) _______________ energy that transfers between objects

due to _____________ differences.

Heat ALWAYS flows from a ___________ object to a ___________ object.

Heat will continue to flow until the temperature of both objects is the same (________________________________________).

The unit of measurement is ________________

Specific Heat (_____) amount of energy it takes to raise the temperature of ____________ of a substance by _____________.

Every substance has its own specific heat because it has a different arrangement of atoms

The spec. heat of many substances can be found in your ref. pack.

Things that heat up or cool off ____________ have __________ specific heats.

Cp (water) = 4.18 J/g°C

(do not take much energy to change the temp)

Things that heat up or cool off ____________ have ___________ specific heats.

Cp (sand) = 0.830 J/g°C

(take a lot of energy to change the temp)

Why does water have such a high specific heat?

___________ bonds that hold one water molecule to another water molecule are _____________ so it takes _________ energy

to break the bonds. Metals have __________ bonds (remember the “sea of e-) and do not need as much energy to break them.

The high specific heat of water helps __________________ global climate because the water in the ocean _________________

changes in temperature

How do you calculate heat (change in thermal energy)?

q = ___________ (measured in _____________) equation

m = __________ (measured in _____________)

cp = __________ (measured in _____________)

ΔT = ____________________ (measured in ____)

Examples:

1. A residential water heater raises the temperature of 125,000 grams of liquid water from 25.0oC to 55.0oC. How much heat was

applied?

2. A 10.0 gram piece of Titanium metal is heated from 27.5oC to 1660.0oC. How many joules of heat must have been applied?

Heat equation (q = m cp T) variations:

Solve for massSolve for specific heatSolve for change in temperature

If asked to solve for Tf or Ti, solve for ΔT. ΔT = Tf - Ti

Examples:

1. A 352 g sample of an unknown substance was heated from 40.0°C to 100°C. In the process, the substance absorbed 8120 J of

energy. What is the specific heat of the substance? ID the unknown.

2. A 4.50 g nugget of pure gold absorbed 276 J of heat. What was the final temperature of the gold if the initial temperature was

25°C?

Calorimetry

Calorimetry process of measuring the amount of ___________________________ by a

substance/chemical reaction

A _________________ is a device that can measure how much heat is released or absorbed.

Allows for _________________ determination of ______

If the water heats up, the system (sample) ______________________

qsystem = _______ qwater = ______

The heat absorbed by the surroundings is ______________ to, but has the __________ sign

of, the heat released by the system so:

____________ = _____________

If the water cools, the system (sample) ________________________ qsystem = _______ qwater = ________

Steps to solve calorimetry problems:

1. Calculate qwater ___________________________

2. Calculate qsystem ___________________________

Examples:

1. When a 4.25-g sample of solid NH4NO3 dissolves in 60.0 g of water in a calorimeter, the temperature drops from 21.00°C to

16.90°C. Calculate the heat change for the solution process.

2. When 25.0 mL of water containing 0.025 mol HCl at 25.0°C is added to 25.0 mL of water containing 0.025 mol NaOH at 25.00°C

in a calorimeter, a reaction occurs. Calculate the heat change during this reaction if the highest temperature observed is

32.00°C. **Assume the densities of the solutions are 1.00 g/mL. ex. 10g = 10mL**

The qsystem that is calculated using data from a calorimeter may be used to calculate the specific heat of a metal and ID an unknown metal.

Example:

A 12.48 g sample of an unknown metal, heated to 99.0 °C was then plunged into 50.0 mL of 25.0 °C water. The temperature of the water rose to 28.75 °C.  Identify and find the specific heat of the unknown.

1. Identify all variables

2. Solve for qwater

3. Solve for qsystem (In this case system is the metal)

4. Use qmetal to solve for specific heat

5. Use reference packet and cp to identify the metal

Lesson 2 – Thermochemistry

Thermochemistry Study of energy changes that occur during ___________________________ and ________________________

Endothermic - Process that _____________________ heat

Heat flows ___________ the system (+q) ______thermic ______thermic

Label +q & –q for each diagram

Heat _________________ the surroundings (-q)

Surroundings feel _________

Exothermic - Process that _______________________heat

Heat flows ___________ the system (-q)

Heat ________________ the surroundings (+q)

Surroundings ________________________

Enthalpy (H) the heat content of a system

units for enthalpy are _____________

ΔH ____________________

assuming pressure is constant, ___________

_____thermic = ___ ΔH _____thermic = ___ ΔH

ΔH & Changes of State

Change in state always involves a _____________________________

Endothermic changes of state absorb heat energy, increasing in temperature

__________________, ____________________, ______________________

As more heat is added the temperature _________________, meaning the particles

are moving _______________.

To make a substance melt or vaporize you continuously add heat to:

*increase the ______________ of the molecules

*__________ the (IMFs) attractions between molecules causing them to separate

Melting (________________)

The __________________ is the amount of heat needed to melt ______________ of a substance at standard pressure.

Heat of Fusion (Hf) of water is ________________. **IN YOUR REFERENCE PACKET TOO**

Equation to solve for heat absorbed during melting: __________________________

Examples:

1. How much heat is added when 15.7 moles of water melts?

2. In the diagram, how much heat is needed for the ice to melt?

Vaporization/Boiling

The __________________ is the amount of heat needed for _________ of the substance to change from liquid to gas at standard

pressure.

Heat of Vaporization (Hv) of water is __________________ **IN YOUR REFERENCE PACKET TOO**

Equation to solve for heat absorbed during boiling: __________________________

Example:

How much heat is absorbed when 24.8 g H2O at 100.0 oC is converted to steam at 100.0 oC?

Exothermic changes of state release heat energy, decreasing in temperature

__________________, ____________________, ______________________

As more heat is removed the temperature _________________, meaning the particles

are moving _______________.

To make a substance condense or freeze you continuously remove heat to:

*decrease the ______________ of the molecules

*__________ the (IMFs) attractions between molecules causing them to _________

Heating/Cooling Curves – show the change of state over time that occurs with the addition or removal of heat energy

HEATING curve for water – considered _____thermic because these phase changes ____________ heat

* Heat can be transferred even if there is no change in state

* During a phase change, the temperature remains

______________. This is because the heat being added is

used to ___________________ holding the molecules

together ______________ the temperature.

* During a phase, KE is _____________ (temp is increasing).

* During a phase change, KE is ________ and PE is __________.

line segments for HEATING curve of water

1

2

3

4

5

phase or phase change

Which phase/phase change?

Description of what is occurring

What is happening to KE &/or PE?

Cp for H2O

Equation to calculate energy

The total amount of heat absorbed is the sum of all five equations: qtot= q1+q2+q3+q4+q5

Why does it take more time (longer line) & energy (2260 J versus 334 J) for vaporization of water to occur than melting?

COOLING curve for water – considered _____thermic because these phase changes ____________ heat

* _________may be used to determine amount of heat released during

condensation

* _____ may be used to determine amt. of heat released during freezing

LABEL each section of the COOLING curve

* During a phase, KE is _______________ (temp is decreasing).

* During a phase change, KE is _____________ and PE is decreasing.

LABEL the curve with KE & PE

How much heat is released when 275 grams of water freezes?

ΔH & Chemical Reactions Chemical reactions always involves a change in heat energy

Endothermic Reactions

C(s) + H2O(g) + 113 kJ CO2(g) + H2(g)

Heat energy is written in the equation as a ___________ since it is coming in/being used.

ΔHrxn = +113 kJ meaning 113kJ are _____________

Potential Energy diagram

__________________ because………

1. Products have ___________energy than the reactants

2. ΔH is ___________________

Exothermic Reactions

C3H8 + 5O2 3CO2 + 4H2O + 2043 kJ

Heat energy is written in the equation as a _____________ since it is released/produced.

ΔHrxn = -2043 kJ meaning 2043 kJ of heat is _____________

Potential Energy diagram

__________________ because………

1. Products have ___________energy than the reactants

2. ΔH is ___________________

Thermochemistry & Stoichiometry

If you know the ΔH for a balanced equation, you may determine the amount of energy ______________________ by a reaction.

ΔH (enthalpy) is proportional to the coefficients for a balanced equation, therefore they may be used to write conversion factors.

2 H2O2(l) 2 H2O(l) + O2(g) Hrxn = -190 kJ

2 mole H2O2 = -190 kJ 1 mole O2 = -190 kJ 2 mole H2O = -190 kJ

Examples:

1. How much heat will be released if 1.0 g of hydrogen peroxide (H2O2) decomposes in a bombardier beetle to produce a steam

spray?

2. How much heat is transferred when 9.22 g of glucose (C6H12O6) in your body reacts with O2 according to the following

equation? C6H12O6(s) + 6O2(g) 6CO2(g) + 6H2O(l) Hrxn = -2803 kJ

3. How much energy will be required to extract 59.5 grams of tin?

SnO2(s) + 4NO2(g) + 2H2O(l) + 192 kJ Sn(s) + 4HNO3(aq) Hrxn = ____________