Energy transfers in solutions

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  • Energy transfers in solutions
    • When a reactions takes place in a solution energy is transferred to or from the solution.
    • We can do the reaction in an insulated container to reduce any energy transfers to the surroundings.
    • We can measure the temperature change of the solution and use this to calculate the energy change using the equation Q=m*c*deltaT
      • In these calculations we assume the solutions behave like water. This means that 1cm cubed of solution has a mass of 1g and the specific heat capacity of the solution is 4.2J/g'C
        • Worked example: A student added 25cm cubed of dilute nitric acid to 25cm cubed of potassium hydroxide solution in a polystyrene cup. He recorded a temperature rise of 12'C. Calculate the energy change. Q=m*c*deltaT volume of soultion= 25+25=50 energy change= 50*4.2*12= 2520J= 2.52kJ
    • When a solid is added to water or an aqueous solution we assume that the volume of the solution does not change, we also assume that 1cm cubed of solution has a mass of 1g and the specific heat capacity as water
    • If we know the number of moles involved in the reaction for which we have calculated the energy change we can calculate the energy change for the reaction in kJ/mol.

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