Energy and Percent Yield

• enthalpy is the energy stored in chemical bonds
• symbol of enthalpy is H
• unit of Joules is J
• change in enthalpy is delta H
• in exothermic reactions enthalpy increases
• in endothermic reaction enthalpy increases

Calorimetry:

-to experimentally determine the heat released we need to know 3 things

1. temperature change deltaT

2. Mass. (m)

3. specific heat capacity (C) --> ability to hold heat

equation: H = mCT

Example:

- Calculate the heat required to warm a cup of 400g of water (c=4.8J/g celsius) from 20 to 50 degrees

H= mCT

H= (4.oo)(4.18)(30)

H= 50160 J --> 50.2 kJ

PERCENT YIELD

• the theoretical yield of a reaction is the amount of products that should be form
• the actual amount depends on the experiment
• the percent yiels is like a measure of success

- how close is the actual amount to the predicted amount?

    %yield = actual              x 100

                   theoretical

Nicole H