Chemistry Thermochemistry.

Define thermochemistry

the study of the energy changes that accompany physical and chemical changes in matter

Define thermal energy

the energy released by the surroundings in a chemical reaction as a result of the motion of the molecules

define a chemical system

a set of reactants and products being studyied in a chemical equation

Define surroundings

All matter around the system responsible for absorbing or releasing thermal energy - usually water

What happens when a reaction occurs?

heat (q) is transferred between the system and the surroundings

Define exothermic and endothermic

exothermic: the system releases energy to the surroundings (- delta h, but positive q) - reactants at higher energy than products - usually feel cold

Endothermic: The system absorbs energy from the surroundings (+delta h, but - q) - products at higher energy than reactans - usually feels hot

What happens when the surroundings absorb enegy from the system?

its temperature increases as well

Define open system, isolated system and closed system

Open system: a chemical reaction that produces gas - energy and matter can flow in and out of the system.

isolated system: neither matter nor energy can move in or out of the system

closed system: energy can move in or out of the system, but not matter - calorimeter.

How do you calculate heat transfer

using q=mct
where m is the mass in g, t is the change in temperature (final-initial) and c is the specific heat capacity of the surroundings (usually water)

what is the specific heat capacity for water

4.18 j/mol*ºC

what is the unit of q

Jules

How to convert Jules to KJ

divide by 1000

How to calculate mass given density

mass = volume * density in aqueous solutions

Define enthalpy change

the difference in enthalpy between reactants and products during a reaction. (delta H)

what is the relationship between q and delta H

when q is positive, delta H is negative

define molar enthalpy

the enthalpy change associated with a physical, chemical or nuclear change involving one mole of a substance (delta Hx)

how to calculate molar enthalpy

delta Hx = delta H/moles