Tracey Zhang 1A
The Relationship Between Temperature and Reaction Time in a chemical
reaction between magnesium and hydrochloric acid
Introduction:
One of the many factors that affect the rate of reaction is temperature; an increase in
temperature increases the average kinetic energy of molecules and increases the
energy with which they collide while a decrease leads to the opposite. This means
an increase in temperature leads to greater instances of collision between
molecules, increasing reaction rate. Thus, for our experiment, we decided to test
how increasing the temperature of the chemical reaction affects the rate of reaction.
For our chemical reaction, we used hydrochloric acid and magnesium because this
common chemical reaction occurs in a short amount of time (less than 1 minute)
and the materials are easily attainable.
Research Question:
How will changing the temperature of hydrochloric acid affect the rate of reaction
between hydrochloric acid and magnesium?
Chemical equation for reaction in investigation:
Mg(s) + 2HCl(aq) = MgCl2(aq) + H2(g)
Hypothesis:
If the temperature of hydrochloric acid is changed in a chemical reaction between
hydrochloric acid, then a higher temperature creates a faster rate of reaction,
because a higher temperature indicates there is greater heat energy necessary in
chemical reactions.
Variables:
Independent Variable: Temperature of hydrochloric acid
Dependent Variable: Reaction time/Rate of reaction (calculated dependent
variable)
Experimental Groups: 30˚C, 40˚C, 50˚C, and 70˚C
Controls: same amount of magnesium used, same amount of hydrochloric acid used,
same number of moles of hydrochloric acid, same container type/size, method of
measuring reaction time
Materials:
-
4 magnesium strips (1/2 cm x ½ cm per strip)
2 mol HCl (30.0 mL per; 4 batches )
-
Stopwatch
Heating plate
Thermometer
Graduated cylinder 50.0 mL
200.0 mL beaker
Diagram:
Procedure:
1. Using the graduated cylinder, measure 30.0 mL of 2 mol dm-3 hydrochloric
acid and pour it into the beaker
By measuring out 30.0 mL of 2.0 mol dm-3 hydrochloric acid, we are ensuring
that in each of the chemical reactions between magnesium and hydrochloric
acid that the amount of hydrochloric acid remains constant.
2. Place the beaker filled with hydrochloric acid on the heating place and, using
the heating plate, heat the hydrochloric acid up to 30.0˚C
30˚C effectively becomes the first of the four temperatures in the experimental
group that the hydrochloric acid will be heated up to.
3. Place the thermometer in the hydrochloric acid to ensure the temperature is
at 30˚C.
The heating plate’s temperature reading may be slightly inaccurate so using
the thermometer would ensure the temperature of the hydrochloric acid is at
the necessary measurement.
4. Place the ½ x ½ cm strip of magnesium into the hydrochloric acid.
Each strip of magnesium must be of lengths ½ x ½ cm, a constant, to ensure
each reaction is the same.
5. Start the stopwatch and measure the amount of time it takes for the reaction
to complete itself, which occurs when all visible fizzing inside the beaker
stops and the magnesium strip has completely dissolved.
This method of measuring reaction time must remain constant for each of the
trials to ensure the trials have only one variable constant—temperature.
6. Record the time obtained from step 5.
7. Repeat steps 2-6 using different temperatures for step 3 (40.0˚C, 50.0˚C, and
70.0˚C)
Data Collection:
Quantitative Observations:
Table 1: The Time taken for a Chemical Reaction to Begin and Finish under
Different Temperatures
Temperature (˚C) ±0.05
30.0
40.0
50.0
70.0
Time (s) ±0.01
33.75
18.06
16.35
13.50
Qualitative Observations:
Table 2: Qualitative Observations During Chemical Reactions between Magnesium
and Hydrochloric acid
Temperature (˚C)
30.0
40.0
Qualitative Observations
 Produces bubbling
 Bubbles at a relatively slow rate
 Magnesium strip becomes shinier and smaller as time
elapses
 Magnesium strip moved around in the hydrochloric acid
during reaction
 Produces bubbling
 Bubbles at a faster rate than the reaction at 30˚C

50.0
70.0
Magnesium strip becomes shinier and smaller as time
elapses
 Magnesium strip eventually completely dissolves, stopping
the bubbling and ending the chemical reaction
 Magnesium strip remains relatively still during bubbling
 Produces bubbling
 Bubbles at a faster rate than the reaction at 30˚C and 40˚C
 Magnesium strip becomes shinier and smaller as time
elapses
 Magnesium strip eventually completely dissolves, stopping
the bubbling and ending the chemical reaction
 Magnesium remained largely still during chemical reaction
 Produces bubbling
 Bubbles at a much faster rate than all previous
temperatures
 Magnesium strip remained relatively in the same position
 Magnesium strip visibly gets smaller at a quick rate
 Magnesium strip becomes shinier as it dissolves
Processed Data:
Example of Calculating Percent Uncertainty:
(Uncertainty/Measured Value) x 100 = (0.01/33.75) x 100 = 0.030%
Table 3: The Percent Uncertainties of Temperature and Time Values used in the
Chemical Reaction
Temperature (˚C)
±0.05
30.0
40.0
50.0
70.0
Percent
Uncertainty of
Temperature
(%)
0.17
0.13
0.10
0.071
Time (s) ±0.01
Percent
Uncertainty of
Time (%)
33.75
18.06
16.35
13.50
0.030
0.055
0.061
0.074
Example of Calculating rate of reaction:
Time of reaction at 30˚C = 29 s (in accordance to the curve of best fit on Graph 1)
Reaction rate = 1/time = 1/29 s = 0.0345 s-1
Table 4: The Relationship between Temperature and Rate of Reaction
Temperature (˚C) ±0.05
Rate of Reaction (1/time) (s-1)
30
0.0345
40
0.0455
50
0.0588
70
0.0833
This table allows us to compare the temperature with reaction rate
Graph 1: The time for a chemical reaction between magnesium and hydrochloric
acid to occur under different temperatures
40
35
Reaction Time (s)
30
25
20
15
10
5
0
0
10
20
30
40
50
Temperature (˚C)
60
70
80
Graph 2: The Relationship between Reaction Rate (1/time) and Temperature
Reaction Rate (1/time) (s^-1)
0.09
y = 0.0012x - 0.0029
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
0
20
40
Temperature (˚C)
60
80
Conclusion:
The results of this experiment supports the hypothesis because as the temperature
of the hydrochloric acid increases, the reaction rate increases, meaning that there is
a direct relationship between the two. Thus, we have achieved the aim of our
experiment, which is to determine how the temperature of the hydrochloric acid
affects the time for a reaction between hydrochloric acid and magnesium to occur.
From the raw data shown in Table 1, the first point shows that at a temperature of
30˚C, it takes approximately 33.75 seconds for the reaction to completely finish. The
next trial at a temperature of 40˚C took 18.06 seconds, which is nearly half the time
of the reaction at 30˚C. The next chemical reaction occurred at a temperature of
50˚C, which resulted in a reaction time of 16.35 seconds. Thus, from 40˚C to 50˚C,
the reaction time decreases by only 1.71 seconds unlike the much larger decrease in
time from 30˚C to 40˚C (15.69 s difference). Finally, at 70˚C, the reaction time is
13.50 seconds. With each successive growth in temperature, we can see that the
reaction time decreases, indicating a faster rate of reaction at a higher temperature.
This is illustrated in Graph 1, which compares temperature to reaction time.
In order to compare the reaction rate with respect to temperature, I created Table 4
and Graph 2 comparing 1/time, or the reaction rate at each different temperature.
Using the times garnered from the curve of best fit in Graph 1, we can see a general
trend line moving upward. This indicates that as temperature increases, the rate of
reaction also increases at a relatively similar increments, with the trend line being y
= 0.001x – 0.002. Graph 2 indicates that as temperature increases, the rate of
reaction increases along with it. As shown in Table 4, at a temperature of 30˚C, the
rate of reaction is only 0.0345 s-1. By 40˚C, the reaction rate increases to 0.0455 s-1,
an increase of 0.011 s-1. At 50˚C, this trend continues, with reaction rate increasing
by 0.0133 up to 0.0588 s-1. Lastly, at 70˚C, the reaction rate continues to increase,
following the equation of the indicated trend line. Thus, from the calculated rate of
reactions, Graph 4 illustrates that as temperature increases, the rate of reaction also
increases, affirming our hypothesis.
Evaluation:
Overall, our results generally corresponded with our expected results because a
greater amount of energy is given initially in the reaction when the temperature is
higher. However, we expected the relationship between temperature and reaction
time to be linear, with an increase in temperature yielding the same amount of
decrease in reaction time at every value. In reality, the relationship between
temperature and reaction looks more like a curve, as illustrated by Graph 1. That
means an increase in temperature does not always create a constant increase in
reaction time.
Lastly, to obtain more accurate experimental results, next time I would use a smaller
amount of hydrochloric acid, having a large amount results in some of the
magnesium being only partially submerged while other magnesium strips are fully
submerged, affecting the reaction time. Hopefully, this would allow for the
experiment to be repeated in multiple trials and garner similar results.
Bibliography:
Helmenstine, Anne Marie. "Factors That Affect the Chemical Reaction
Rate." About.com Chemistry. About.com. Web. 02 Mar. 2012.
<http://chemistry.about.com/od/stoichiometry/a/reactionrate.htm>.
"RATES OF REACTIONS." Chem4Kids.com: Reactions: Rates of Reaction. Chem4Kids.
Web. 04 Mar. 2012. <http://www.chem4kids.com/files/react_rates.html>.
"Rates of Reaction." Gondar Design Science. Web. 04 Mar. 2012.
<http://www.purchon.com/chemistry/rates.htm>.
"The Effect of Temperature on Rates of Reaction." Chemguide: Helping You to
Understand Chemistry. Web. 03 Mar. 2012.
<http://www.chemguide.co.uk/physical/basicrates/temperature.html>.