# Calorimetry Worksheet Answers - PDF by xbt29315

VIEWS: 225 PAGES: 3

• pg 1
```									                                              Name                                                  Period

CALORIMETRY
1)      Define these terms:
a.       Heat = flow of thermal energy from higher temp to lower temp
b.       Temperature = measure of the average kinetic energy of a sample
c.       The Law of Conservation of Energy = Energy is neither created nor destroyed only transferred.
d.       Specific Heat = energy required to raise the temp of 1 gram of substance by 1ºC
e.       Heat of Fusion = energy required to melt 1 mole of solid
f.       Heat of Vaporization = energy required to boil 1 mole of liquid
g.       Endothermic = gain of heat energy
h. Exothermic = loss of heat energy
2)      A student performs an experiment in which 45.0 grams of metal is heated to 80.0ºC. the metal is
transferred to a cup of water. The water gains 9000 kJ of energy as the metal cools to 40ºC.
a.       Is the process endothermic or exothermic for the water? endothermic
b.       Is the process endothermic or exothermic for the metal? exothermic
c.       Determine the specific heat of the metal. .05 J/gºC
3)      If you did a calorimetry experiment in which you put a cube of iron metal that is very hot into a cup of
room temperature water, the _____water_____ would get warmer, and the ___metal___ would get cooler
as heat flows from ___higher temp_______ to ___lower temp_________.
4)      The larger the value of _specific heat__ of a substance, the more heat it requires to even get warmer,
meaning to raise the temperature 1°C. Conversely, it also means it will gives off more energy when the
same substance cools 1°C compared to other substances with lower __specific heat__ values. The
lower the _specific heat_ value of a substance means that it will not require much energy to heat and
lose much energy to cool. Water has a very high _specific heat__ values compared to many
substances. It takes a longer amount of time (and more heat) for water to start feeling warm as
opposed to the metal pan it is being boiled in.
5)       A 100 g chunk of metal with a specific heat of 0.24 J/g°C is heated from 20°C to 40°C. What is the total
energy change, or heat gained, of the chunk of metal (write all units)? Q = 100g • .24J/gºC•20ºC
6)      A 50 g metal cube loses 1350 J (and is expressed as -1350 J) as it is cooled from 150°C to 120°C. What is
the specific heat of this metal substance (write all units)? -1350 J = 50 g C -30ºC…solve for C
7)      When you want to know the amount of energy change (or heat gained or lost) when a substance
CHANGES PHASES (and not only changing temperatures…getting warmer or cooler), you must use heat
of __Fusion__ (ΔHf) or heat of __Vaporization___ (ΔHv) values.
8)      ΔHf is the heat gained (when going from solid to liquid or melting) or lost (when going from liquid to solid
or freezing) of one MOLE of a particular substance.
9)      ΔHv is the heat gained (when going from liquid to gas or boiling) or lost (when going from gas to liquid or
condensenation) of one MOLE of a particular substance.
10)     Write the equation you would use to figure out the heat released or absorbed when changing phases
from solid to liquid or vice versa.__q = n ΔHf _________________________________
11)     Write the equation you would use to figure out the heat released or absorbed when changing phases
from liquid to gas or vice versa. q = n ΔHv ___________________________________
12)     You melt 72 g of ice. The ΔHf value of water is about 6 kJ/mol. How much heat is released/absorbed?
72 g | 1 mol | 6 kJ = 24 kJ
| 18 g | 1 mol
13)     You condense 3.6 g of steam. The ΔHv value of water is about 41 kJ/mol. How much heat is
released/absorbed? Is heat released or absorbed?
3.6 g | 1 mol | 41 kJ = 8.2 kJ
| 18 g | 1 mol

ACID-BASE TITRATION
14)   An acid releases ____H+_________ ions when put in solution (in water).
15)   A base releases _____OH-________ ions when put in solution (in water).
16)   Strong acids release _all of __H+__ ions; weak acids release some all of __H+__ ions.

1

17)    Strong bases release __all_ of _OH-___ ions; weak bases release __some of __OH-_ ions.
18)    Neutralization is when an acid and a base is mixed together in solution and produces __salt__ and
__water___. The pH should be ___7__. For this to happen, the __H+__ ions from the acids should pair up
with __OH-__ ions in matching amounts. An technique used where you add just enough acid (and thus
__H+__ ions) to base (and thus match the number of _OH-___ ions) is called titration___.
19)    A common instrument with graduated volume readings and a stopcock called a __buret__ is used in
titration__ experiments. This is because you can use the stopcock to control the amount of acid (or
base) added to the base (or acid). You then know how much you used by looking at the final volume
reading and the initial volume reading and _difference between __ the two to get the total volume used.
20)    You know when you added just the right amount of acid to a base (or base to an acid) when it changes
_color_ (in our experiments, to a very light _pink__). This substance that changes _color_ is called an
indicator_. The one we used in our experiments is called phenolphthalein____.
21)    We use these experiments because we may know the concentration, measured in _M or
mole/liter______ and sometimes written using [ ], of, let’s say a base, but maybe we don’t know the
concentration of an acid (this could work the other way where we don’t know the concentration of a
base and use an acid). Knowing how much volume of both the acid and the base used, we can
calculate the missing concentration value, measured in __M or moles/liter__ (units are ________). Write
the equation we use to calculate the concentration of something unknown. M = moles/liters
22)    Solve the following titration problem. You have a 0.8 M solution of a base. It takes 40 mL of the base to
react with 20 mL of an unknown acid to get the very light pink color we all like. What is the
CONCENTRATION of the acid? Show the work and write all units.
Ma • 20 mL = .8 M • 40mL Ma = 1.6 M

ICE CREAM ACTIVITY
23)    In the ice cream lab, we used something to decrease the temperature of the milk, sugar and vanilla
mixture. This was _ice_ in which we added _salt_. Why? _Salt lowers the melting temperature of the ice.
24)    Heat was transferred from the _milk mixture to the _ice_ in the ice cream activity. The heat transferred
was used to change the _temperature______________________ (make colder) of the milk mixture and also
to change the _phase (from liquid to solid). If you had to, you would use both the _temperature
change_ equation AND the _phase change_ equation to figure out the total energy change or heat
transferred in this activity.
POLYMERS
25)    A _polymer is a long chain of smaller _monomers_ connected together in a repeating pattern. Many
molecules in nature, like DNA, protein, fats, and carbohydrates, are HUGE only because nature takes
simple molecules and connects them to make longer strings of compounds so that they are thousands
of atoms in size.
26)    Since these long chains are just repeating units of smaller molecules, they tend to be stretchy and
pliable (moldable like glue, putty, plastic, rubber, synthetic fibers).
27)    Identify the repeated units and circle them in the following molecules. CH2CHBr
~CH2CHBrCH2CHBrCH2CHBrCH2CHBrCH2CHBrCH2CHBrCH2CHBrCH2CHBrCH2CHBr~

2

28)     To form these longer chains from smaller molecules in a repeating pattern, many times, another
chemical is used to bind the smaller chains to make bigger chains. In the glue and Borax lab, _borax__
was used as the binding/linking agent and _white glue_ was used to make longer chains.
Circle the binding/linking agent and label it correctly with either Borax or glue. Draw a box around the polymer
chain and label it correctly with either Borax or glue.

CRYSTALS
29)   Much like polymers, crystals form repetitive links and patterns of atoms and molecules. However,
crystals tend to form more geometric_ patterns and organized_ arrangements like cubic, tetragonal,
and hexagonal forms.
30)   Substances like quartz, rock salt and diamonds are all examples of crystals. A snowflake is just water
freezing and forming organized_ arrangements of molecules in the solid form and forming geometric__
shapes.
31)   _Seed crystals or nucleation agents_ are required for crystals to form. It is a place or particle which
solutes of substances start latching onto and grow bigger as more solute particles clump together and
form larger and more geometric_ shapes. In the microscope crystal lab, what region of the solution
drop acted as _crystallization site_? _the edge of the drop__ What about in your rock candy? _the seed
crystals on the stick or string.
32)   A single crystal unit has a particular shape. But only when it grows as the solute particles attach in
increasing amounts do you get various and interesting shapes like a snowflake. Remember, no two
snowflakes are alike! This is because water particles can arrange in many different ways.

3

```
To top