THERMO CHEMISTRYCHAPTER 11.2 CALORIMETRY

In a chemical reaction energy is required to break and reform bonds. If there is more energy released than used this is an exothermic reaction, if the reaction pulls energy from the surrounding environment it is an endothermic reaction.

HEAT = ENERGYHeat, thermal energy is the energy of motion of all the molecules and atoms. The greater the thermal energy, the greater the kinetic energy of its particles. This energy can be transferred to other objects, but it cannot be created or destroyed.

To study the energy created in these chemical reactions, the environment must be controlled. An ideal scenario is when all matter and energy are contained in the reaction to be accurately measure. When neither matter or energy can move in or out, this is called an isolated system.

A calorimeter is a device used to isolate a chemical reaction from the surrounding environment. Often a simple calorimeter can be made from a Styrofoam cup containing a measured quantity of water and a thermometer.

When measuring the energy change a few variables must be known to fit in to the equation.

c, specific heat capacity of the substance (in a water based solution c = 4.19J/(g* o C)

m, mass of the substance Δt, is the change in temperature in oC (but kelvin will also work) Q, energy, measured in Joules (J)

Specific heat capacities include:

Certain assumptions must be made:

1. That the water changes temperature, but the container, lid and stir stick do not. (isolated)

2. Dilute solutions have the same specific heat capacity of water (4.19)3. The mass of dilute solutions is approximately that of water (1ml = 1g)

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