Thermochemistry: Enthalpy Changes in Simple Processes
Introduction The primary objective of this lab is to be able to determine the specific heat of a reaction by using a calorimeter. A calorimeter is a device used to determine the specific heat of chemical reaction or a physical change. The specific heat a reactions is used to refer to the amount of heat that is lost or gained when one gram of a particular substance increases or decreases by one degree Celsius. When a chemical reaction occurs in an open container most of the energy gained or lost is in the form of heat. Almost no work is done (i.e. nothing is being moved). Heat flows between the system and surroundings until the two are at the same temperature, when a chemical reaction occurs in which the system absorbs heat, the process is endothermic (it feels cold). When a chemical reaction occurs in which the system produces heat it is exothermic (it feels hot)
Under conditions of constant pressure the heat absorbed or released is termed enthalpy (or "heat content"). We do not measure enthalpy directly, rather we are concerned about the heat added or lost by the system, which is the change in enthalpy (or ΔH The quantity of heat gained or lost by a system, ΔH, is dependent upon, the mass, m, of the system: the more massive an object the more heat needed to raise its temperature, the change in temperature, (ΔT): the larger the temperature change in a system the more heat exchanged, and the nature of the substance(s) making up the system. The last quantity is defined by the heat capacity of the system. For a given substance, the specific heat capacity is defined as the quantity of heat needed to raise 1 gram of the substance by 1 degree Celcius. Specific heat capacity has units of joules per degree Celcius per gram, J.g-1.ºC-1.The three quantities combine to give the quantity of heat gained, or lost, by a system:
ΔH = mass x Specific heat capacity x ΔT
ΔT represents the difference between the enthalpy of the system at the beginning of the reaction compared to
Under conditions of constant pressure the heat absorbed or released is termed enthalpy (or "heat content"). We do not measure enthalpy directly, rather we are concerned about the heat added or lost by the system, which is the change in enthalpy (or ΔH The quantity of heat gained or lost by a system, ΔH, is dependent upon, the mass, m, of the system: the more massive an object the more heat needed to raise its temperature, the change in temperature, (ΔT): the larger the temperature change in a system the more heat exchanged, and the nature of the substance(s) making up the system. The last quantity is defined by the heat capacity of the system. For a given substance, the specific heat capacity is defined as the quantity of heat needed to raise 1 gram of the substance by 1 degree Celcius. Specific heat capacity has units of joules per degree Celcius per gram, J.g-1.ºC-1.The three quantities combine to give the quantity of heat gained, or lost, by a system:
ΔH = mass x Specific heat capacity x ΔT
ΔT represents the difference between the enthalpy of the system at the beginning of the reaction compared to