Investigation into the factors affecting the Heat of Reaction.

Safety

• HCL is irritant - wash skin with cold water if contact occurs
• Wear goggles

Apparatus

• Pipette
• Measuring cylinder
• Polystyrene cup
• Thermometer
• Ruler
• Scissors
• Lid with hole (to fit thermometer in)
• 75 cm magnesium
• 25 ml (x 5)
• Stopwatch
• Beaker

Diagram

Method

• Put 25 ml HCL into measuring cylinder using a pipette
• Cut 5 cm strip Mg using a ruler to measure
• Pour the HCL into a polystyrene cup and then put it into a glass beaker
• Measure temperature of HCL using thermometer
• Put 5 cm of magnesium into cup and put a lid on it with the thermometer inserted in the hole
• Record the temperature at 15, 30, 45 and 60 seconds using a stop watch
• Put results in table
• Repeat the experiment with 10, 15, 20 and 25 cm strips of magnesium using ruler to measure
• Repeat whole experiment to obtain more data and to ensure accuracy

Results

Analysis

I predicted that the longer the length of Magnesium strip used, the greater the increase in temperature.  My prediction proved true because both the Line Graph and Bar Chart show a larger increase in temperature every time the length of Magnesium strip increases, (the Bar Chart shows a larger bar for every increase in the length of Magnesium strip which means/shows a larger increase in temperature). The Line Graph shows a steady line of temperature change according to the length of Mg up to 15cm Mg where the extra 5cm of Mg would be thought to add roughly 14oC on to the temperature change and it shows only an 8oC difference in temperature.  The Bar Chart and Line Graph are very much closely related for which the Line Graph shows the line of correlation/pattern of the Bar Chart, (if a cross was to be drawn on the top right hand corner of every bar in the Bar Chart, and those crosses were to be joined up by one smoothly drawn line, that line would look the same as the line of correlation/pattern in the Line Graph).  

Evaluation

I got more unusual results, as the Magnesium strip got larger in length.  At 15cm Magnesium strip the results started to get slightly unusual, where the temperature change was not much more than 10cm Magnesium strip.  The Magnesium strip being more able to fold or bend, as the Magnesium strip gets larger can explain not much of a difference in temperature change because if part of the Magnesium strip is folded there is less surface area and therefore less Mg particles to react with the HCL which means that there is less heat given off (temperature change) as this is an exothermic reaction.  Less surface area is thought to be as the most likely reason for less temperature change.   This explanation is then contradicted at 20cm length Magnesium strip where it created the 2nd largest temperature change and the largest temperature change for how long the Magnesium strip is.  However, the 20cm Magnesium strip used could have been the only Magnesium strip that had not folded/bent over at all when the experiment was carried out which means maximum surface area for the length of Magnesium strip and therefore more heat given off because of more Mg particles exposed to the HCL, creating more of an exothermic reaction.

There is not much further work that could be done to obtain more evidence and accurate data apart from using different and more professional equipment.  The main problem that most definitely occurred during this experiment is heat loss.  Heat loss can be resolved by using a lid with a seal to go on the polystyrene cup and with a hole specially designed to fit the thermometer, elastic to stop heat loss through the otherwise gap around the thermometer.