(P) Energy transfers

• You can measure the amount of energy released by a chemical reaction (in solution) by taking the temperature of the reagents, mixing them in a polystyrene cup and measuring the temperature of the solution at the end of the reaction
• A reagent is a compound or mixture added to a system to cause a chemical reaction or test if a reaction occurs. A reagent may be used to find out whether or not a specific chemical substance is present by causing a reaction to occur with it
• The biggest problem with energy measurements is the amount of energy lost to the surroundings. You can reduce it a bit by putting the polystyrene cup into a beaker of cotton wool to give more insulation, and putting a lid on the cup to reduce energy loss by evaporation

  
• The method for measuring energy transferred works for neutralisation reactions or reactions between metals and acids, or carbonates and acids. You can also use this method to investigate what effect different variables have on the amount of energy transferred - e.g. the mass or concentration of the reactants used
• Here's how you could test the effect of acid concentration on the energy released in a neutralisation reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH):

  1)Put 25 cm^3 of 0.25 mol/dm^3 of hydrochloric acid and sodium hydroxide in separate beakers

  2) Place the beakers in a water bath set to 25°C until they are both at the same temperature (25°C)

  3) Add the HCl followed by the NaOH to a polystyrene cup with a lid

  4) Take the temperature of the mixture every 30 seconds, and record the highest temperature

  5) Repeat steps 1-4 using 0.5 mol/dm^3 and then 1 mol/dm^3 of HCl