ENERGY AND PERCENT YIELD

My face in class today (due to learning something new!)

Today we learned about Energy and Percent Yield.

• Enthalpy is the energy stored in chemical bonds
• The Symbol of Enthalpy is H, Units of Joules (J)
• Change in Enthalpy is ∆H

It is important to remember what Exothermic and Endothermic reactions are. (wikipedia definitions)

EXOTHERMIC: 

The term exothermic ("outside heating") describes a process or reaction that releases energy from the system, usually in the form of heat, but also in the form of light (e.g. a spark, flame, or explosion), electricity (e.g. a battery), or sound (e.g. burning hydrogen).

 

ENDOTHERMIC:  The word endothermic ("within-heating") describes a process or reaction in which the system absorbs energy from the surroundings in the form of heat. Its etymology stems from the Greek prefix endo-, meaning “inside” and the Greek suffix –ther, meaning “heat”.

IN EXOTHERMIC REACTIONS, ENTHALPY DECREASES (HEAT IS BEING RELEASED)

IN ENDOTHERMIC REACTIONS, ENTHALPY INCREASES

Calorimetry: To experimentall determine the heat released we need to know 3 things:

1. Temperature Change (∆T)
2. Mass (m)
3. Specific heat capacity (C)

These are related by the equation: ∆H = mC∆T or ∆H= mC (Tf-Ti)

An example:

Calculate the heat required to warm a cup of 400 g of water (C= 41.8J/g°C) from 20.0°C to 50.0°C.

STEPS:

∆H = mC∆T

∆H =(400g)(4.18J/g°C)(50.0°C-20.0°C)

=50160 J 

Pretty simple stuff right? Too bad the homework is pretty difficult! Wish us luck!

Post by RenRen