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ACTIVITY X-CHEMISTRY-2012-13
ENERGY IS STORED IN MATTER. CHEMICAL REACTIONS REARRANGE
MATTER & AS A RESULT OF CHEMICAL REACTIONS IN A CELL, ENERGY
MAY BE RELEASED, STORED, OR USED TO DO WORK.
CHEMICAL REACTION INVESTIGATION
PRE-LAB ACTIVITY:
When a chemical reaction takes place, something new is produced. Chemical reactions
involve the breaking of bonds, rearrangement of atoms, formation of new bonds. Only the
outer (valence) electrons are involved in chemical reactions.
Chemical reactions occur in the cells of all living things. Chemical reactions are
important to cells for two major reasons. First, they are the only way to form new
molecules that the cell requires for growth & maintenance. Biosynthesis (anabolic)
chemical reactions build large complex molecules from smaller less complex molecules.
For example, biosynthesis reactions build proteins from amino acids and, in turn, build
cells, which build tissues etc. Biosynthesis reactions store energy.
Second, the making and breaking of bonds involves changes in energy. As a result of
chemical reactions in a cell, energy may be stored, used to do work, or released. For
example, Decomposition (catabolic) reactions break down large complex molecules in to
smaller less complex molecules with the release of energy. Organisms can use some of
this energy to do work as it is released during chemical reactions.
Energy is stored in matter or within the bonds between atoms. The food living things eat
is matter.
Think of the process that breaks down food and converts the energy that is released into
another form of chemical energy that the cells can us to carry out activities.
1. What is the name of that process? _______________________________
2. In this process, what did you start with and what did you end up with?
___________________________________________________________
____________________________________________________________
3. Would you consider this process a chemical reaction? ____________
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4. Think of the process that captures light energy and converts it into chemical
energy stored in the overall structure of organic molecules (food). What is the
name of this process?
5. Describe why this process is a chemical reaction. __________________
_____________________________________________________________
_________________________________________________________________
All chemical reactions are accompanied by a change in energy. The energy required to
get a chemical reaction started is called activation energy. Energy is required (absorbed)
to break bonds and energy is released when new bonds form.
If more energy is released from the formation of new bonds than is absorbed (required) in
breaking initial bonds, the reaction as whole releases energy to their surroundings in the
form of heat. Such chemical reactions are called exothermic or exergonic.
If less energy is released from the formation of new bonds than is absorbed (required) in
breaking initial bonds, the reaction as a whole absorbs energy from its surroundings.
These reactions are called endothermic reactions or endergonic.
6. In terms of energy release or energy absorption, what types of chemical reaction
are cell respiration and photosynthesis?
____________________________________________________________________
___________________________________________________________________
7. Based on your above answer can you explain why it feels warm when your in a
crowded room?
______________________________________________________________________
___________________________________________________________________
Keep in mind that chemical reactions happen when two or more substances interact.
These can be atoms interacting, molecules interacting, or ions interacting. These
interactions can involve transfer of electrons between reacting atoms, ions, or molecules
or by sharing of electrons to create bonds.
8. Considering the above paragraph, what determines how an atom interacts in a
chemical reaction?
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________________________________________________________________________
The rate of chemical reactions (the speed at which a reaction happens) depends on how
frequently the reactant molecules are colliding into each other. The higher the number of
collisions the more recombination of molecules will occur. Thus increasing concentration
of substances reacting increases the rate of reaction.
Increasing temperature increases the rate of chemical reactions by supplying the
activation energy required. However, you cannot increase the temperature inside the cell
without killing it.
9. How can a cell increase its chemical reactions without raising temperature? _____
__________________________________________________________________
LAB INVESTIGATION:
MATERIAL:
Clock with second hand
Distilled water
Citric acid 10 ml
Graduated cylinder 100 ml
Hydrogen peroxide 3%
Liver (raw)
2 test tubes
Test tube rack
Thermometer or temperature probe
Graduated cylinder 10 ml
Sodium bicarbonate 6 grams
Stirring rod
PROCEDURE:
PART A
1. Add 5 ml of hydrogen peroxide to a test tube.
2. Place a thermometer into the test tube.
3. Find the temperature of the hydrogen peroxide and record this as the temperature
before adding the liver. You will need to set up a data table.
4. Remove the thermometer from the test tube.
5. Add a small piece of liver to the test tube
6. Replace the thermometer and begin to record the temperature of the hydrogen
peroxide every half minute for six minutes.
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PART B
1. Add 10 ml of citric acid to the second test tube.
2. Place a thermometer or probe into the test tube.
3. Find the temperature of the citric acid and record this as the initial temperature
before adding the sodium bicarbonate. You will need to set up a data table.
4. Remove the thermometer from the test tube.
5. Add 6 grams of sodium bicarbonate to the test tube and mix
6. Replace the thermometer and begin to record the temperature of the solution every
half minute for six minutes
PART C.
1. Graph your results for both hydrogen peroxide and sodium bicarbonate. First
determine the independent and dependent variable and what goes on the X-axis
and the Y-axis (independent always goes on the X axis).
ANALYSIS QUESTIONS:
1. Is there any evidence that energy was released to the environment or absorbed
from the environment when liver was added to hydrogen peroxide? Explain the
reason for your answer.
2. Is there any evidence that energy was released to the environment or absorbed
from the environment when sodium bicarbonate was added to citric acid? Explain
the reason for your answer.
3. Did a chemical reaction take place?
4. What do bubbles indicate?
5. Which reaction was exothermic? Explain using data
6. Which reaction was endothermic? Explain using data
POST LAB ACIVITY:
The rate of chemical reactions (the speed at which a reaction happens) depends on how
frequently the reactant molecules are colliding into each other. The higher the number of
collisions the more combination of molecules will occur. Thus increasing temperature
increases the rate of reaction. However, you cannot increase the temperature inside the
cell without killing the cell.
In this investigation hydrogen peroxide was changed into water and oxygen.
1. If you added liver to an old bottle of hydrogen peroxide in your medicine cabinet
and measured the temperature of the hydrogen peroxide and the temperature
remained the same, what might you conclude?
____________________________
2. Why does hydrogen peroxide bubble when you pour it on a cut?
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______________________________________________________________
______________________________________________________________
______________________________________________________________
Hydrogen peroxide is naturally produced in organisms as a by-product of certain cell
chemical reactions. Hydrogen peroxide is poisonous and can damage cells. It is very
important that cells can change hydrogen peroxide quickly into water and oxygen.
However, cells can’t speed up chemical reactions by increasing temperature without
killing themselves.
3. What did we mix with the hydrogen peroxide? ___________________________
4. Liver is an organ composed of tissues. What are tissues composed
of? _________
Cells contain a certain type of protein called enzymes that can speed up chemical
reactions without raising the temperature. Anything that can speed up a chemical
reaction is known as a catalyst. Thus enzymes are often called biological catalysts.
5. What do you think the liver cells have inside them that helped speed up the
chemical reaction?
_________________________________________________
When a chemical reaction occurs, it can be described by an equation. This shows the
chemicals that react (called the reactants) on the left-hand side, and the chemicals that
they produce (called the products) on the right-hand side. The chemicals can be
represented by their names or by their chemical symbols.
2H2O2--------catalase--------------> 2H2O + O2
The above is the chemical equation for the chemical reaction studied
in this investigation.
6. What are the chemical reactants?
5
7. What are the products of this chemical reaction?
8. How many hydrogen atoms are on the reactants side of
the
equation?
9. How many oxygen atoms are on the reactants side of the
equation?
10.
How many hydrogen atoms are on the product side of the
equation?
11.
How many oxygen atoms are on the product side of the
equation?
12.
Based on your answers to questions 8-11 what conclusion
can you come up with about chemical reactions?
13.Based on your answer to number 12, what is wrong with the equation
below?
Al + O2----- Al2O3
14. What can you add to make it correct?
15. Balance the equations below.
C3H8 + O2 ---> H2O + CO2
C5H12 + O2 ---> CO2 + H2O
Zn + HCl ---> ZnCl2 + H2
16. In the molecule C6H12O6
6
a. How many atoms of each element are there?
17.What information does a chemical equation provide about a chemical
reaction?
18.Balancing chemical equations illustrates one of the most basic laws of
chemistry. What is that law? Define it.
____________________________________________________________
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