Unit 11: Thermochemistry Vocab

chemistry idk

Thermochesmitry:

The study of heat changes that occur during chemical reactions and physical changes of state

Energy:

The ability to do work or supply heat

Different forms of energy

kinetic, potential, heat, thermal equilibrium, temperature, chemical potential energy

Kinetic energy

energy of motion

Heat’s symbol

Q

Heat

a form of energy associated w/ the motion of particles, heat flows from warmer objects to cooler objects

Thermal Equilibrium:

If two objects come into contact w/ one another, heat will move from the warmer object to the cooler object until they the same temperature, at this point thermal equilibrium is reached

When you add heat energy…

molecules move faster; temperature increases

Temperature:

A measure of heat; increase heat, increase temperature, typically measured in Celsius

Chemical Potential Energy:

Stored energy in chemical bonds, depends on the type of atoms and arrangement

Exothermic

Potential Energy is converted to heat (heat is given off - feels hot)

Endothermic

Heat is absorbed and converted to potential energy (feels cools)

Law of Conservation of Energy:

“Don’t play God” rule, energy can neither be created nor destroyed only converted from one form to another

Units of energy:

Joule (J)

calorie (calorie): chemistry calorie

Calorie (cal): food calorie

* 1 food cal = 1000 chemistry cal
* 1 cal = 4.18J

Specific heat of water

4\.184 g/c

Calorimetry

is the accurate and precise measurement of heat change for chemical and physical processes

Calorimeter

measures the amount of heat absorbed or released during these processes

Temperature change is dependent on

Amount of heat added, mass of substances, composition of the substance (specific heat)

Specific heat (c):

Amount of heat required to raise the temperature of 1 gram of a substance by 1°C

q=mcΔt

the formula for finding the heat required to raise the temperature of a substance

q=mcΔt

q= heat (J or cal)

m= mass (grams)

c= specific heat cal/g° or J/g°c

m=q/cΔt

the formula for finding the mass required for a heat increase/decrease

if you don’t have the mass in a problem you can use this or just use q=mcΔt and solve for m

Thermochemical equation:

A chemical equation which includes the nergy used or produced during the chemical reaction

Enthalpy (H) (heat of reaction);

Heat content of a susbtance at a constant pressure

This is the “heat of a reaction” or the heat absorbed or realsed during the chemical reaction

ΔH represents..?

Change in enthalpy

Exothermic reactions can be shown by

the enthalpy being negative and is apart of the products

Endothermic reactions can be shown by

the enthalpy being positive and is apart of the reactants

Heat of the reaction

Amount of energy used or produced for a reaction that includes EXACTLY the number of moles of each substance shown by the coefficients of the chemical equation

Heating curve

Graph of temperature versus time, it describes the enthalpy changes that take place during phase changes

When a solid substance is heated temperature will increase until it reaches its _____________

melting point

The temperature during the melting process is ________

constant

Heating curve problems involve what two calculations

q=mcΔt, used for temperature and dimensional analysis using ΔH, where there is a phase change (flat line)

Molar heat of fusion (ΔHfus)

The amount of energy required to melt a substance (solid -→ liquid)

Molar heat of vaporization (ΔHvap)

the amount of energy required to vaporize (boil) a substance (liquid -→ to gas)

ΔT (and how to calculate: Tf - Ti)

change in temperature

Calorie (captial)

Food calorie

calorie (lowercase)

chemistry calorie

Joule

unit of energy and heat

Hess’s Law:

You can add two or more chemical equations to get an overall equation, AND you can also add the heat changes (ΔHs) to get the overall heat change.

How to add chemical equations?

same substance on opposite sides - CANCEL

two identical on the same side - ADD COEFFICIENT

keep substances on the same side of the arrow in the final equation

How to reverse chemical equation

You can reverse a chemical equation by changing sides with the products and reactants which changes the sign of the heat (if negative positive if positive negative)