Thermochemistry and Types of Reactions Test - 4/24

5 types of chemical reactions

1. Synthesis

2. Decomposition

3. Single replacement

4. Double replacement

5. Combustion

synthesis reaction

• composition or combination reaction

• Substances react to form a compound - “to build”

• Substance + substance yields compound

  • A + B → AB

Synthesis rules: metal oxides + water → ?

Metal hydroxide

Synthesis rules: nonmetal oxides + water → ?

oxyacids

Synthesis rules: Metal oxides + nonmetal oxides → ?

salts

Decomposition reaction

• compound produces 2 simpler substances

• Opposite of synthesis reactions - “break apart”

• Often requires energy (heat, light, or electricity) to occur

• Compound yields substance + substance

  • AB → A + B

Decomposition rules: metal carbonates → ? + ?

metal oxide + carbon dioxide

Decomposition rules: Metal chlorates → ? + ?

Metal chloride + oxygen gas

Decomposition rules: Metal hydroxides → ? + ?

metal oxides + water

Decomposition rules: oxyacids → ? + ?

nonmetal oxides + water

single replacement reaction

• one element replaces a similar element in a compound - ions switch places

• Element + compound yields element + compound

  • A + BC → AC + B

Cationic single replacement reaction

metals (+) switch places

Anionic single replacement reaction

nonmetals (-) switch places

double replacement reaction

• ions of 2 compounds in aqueous solutions switch places to form 2 new compounds - cations (+) switch

• Compound + compound yields compound + compound

  • AB + CD → AD + CB

Result of most double replacement reactions are either (3): formation of a…

• precipitate

• Water (neutralization reaction)

• Gas

Double replacement reactions: formation of water (neutralization reaction)

• reaction between an acid and a base

• Produces a salt (ionic compound) and water → always the products

Double replacement reaction: formation of a precipitate

• produces a precipitate (solid compound) and an aqueous compound

  • Insoluble product = precipitate

combustion reaction

• substances react with oxygen releasing a large amount of energy

• Hydrocarbon + O₂→ CO₂ + H₂O

  • Most common combustion reaction is between a hydrocarbon and oxygen

  • Products will always be carbon dioxide and water

Almost all chemical reactions are accompanied by a…

change in energy

energy is either absorbed or released as heat, also known as…

thermal energy

Thermochemistry is the study of the … as heat during chemical reactions and physical changes

transfer of energy

First Law of Thermodynamics: the total energy of the universe is … and can neither be created nor destroyed; it can only be …

• constant

• Transformed

energy is the … and can take many forms.

capacity to do work

The forms of energy we deal with in chemical reactions are (3):

1. Potential energy is stored energy or the energy of position - energy stored within the bonds between atoms → takes energy to break the bonds of the reactants in a chemical reaction, so the energy is absorbed

2. Kinetic energy is the energy of motion - when the bonds of the reactants are broken, potential energy transforms into kinetic energy

3. Thermal energy (heat)

What happens when a chemical reaction takes place (4)?

1. Bonds of the reactants are broken → takes energy

2. If the energy is not enough to break the bonds of the reactants, the reaction will not occur

3. Then, atoms are rearranged

4. Finally, new bonds are formed (products) → releases energy

Breaking bonds … energy

Forming bonds … energy

• requires

• Releases

Reactants have … stored in the bonds

potential energy

When the reactants undergo a chemical reaction, the atoms are …

rearranged - kinetic energy

products have … stored in the bonds

potential energy

Temperature is a measure of the … of the particles of matter

average kinetic energy

The greater the kinetic energy of particles of matter …

the hotter it feels

K = ?

C + 273

The ability to measure temperature is based on …

energy transfer

Heat is a form of energy that is transferred between matter due to a …

difference in temperature

Heat energy always moves spontaneously from … to …

higher temperature to lower temperature

Heat is usually measured in the SI unit … and is a very small unit of heat → … are commonly used

1 kJ = ? J

• Joules (J)

• Kilojoules (kJ)

• 1 kJ = 1,000 J

calorie (cal) = the quantity of heat needed to …

1 calorie = ? J

• raise the temperature of 1g of pure water 1 degree C

• 1 calorie = 4.184 J

system

Area where the reaction takes place (inside a flask, dish, or other reaction vesicle)

Surroundings

everything outside the system

exothermic chemical reaction

• Reactants → products + energy

  • Release energy

• potential energy stored in the bonds of the reactants is greater than the potential energy stored in the bonds of the products → energy is lost

• Extra energy (thermal energy) is released from the system and into the surroundings → surroundings become warmer

  • Feels hot

endothermic chemical reaction

• Reactants + energy → products

  • Absorb energy

• more potential energy in the bonds of the products than in the bonds of the reactants → energy is gained

• Extra energy is absorbed from the surroundings → surroundings become cooler

• Thermal energy is supplied to the system from the surroundings → feels cold

Negative enthalpy = … of energy

loss

Endothermic or exothermic reaction?

Exothermic reaction

• Products have less potential energy than reactants

• Lost heat energy goes to the surroundings

Endothermic or exothermic reaction?

Endothermic reaction

• Products have more potential energy than reactants

• Gained heat energy comes from the surroundings

Positive enthalpy = … of energy

gaining

activation energy

the minimum amount of energy required to overcome the bond energies of the reactants (break the bonds and get the reaction started)

Calorimetry

measurement of heat flow into or out of a system during a reaction or a physical change

heat released by the system is equal to … by the surroundings

Or, heat absorbed by the system is equal to … by the surroundings

• heat absorbed

• Heat released

In calorimetry, an instrument called a … is used to measure … by the system and its surroundings

• calorimeter

• Heat energy lost or gained

Calorimeter

• insulated device used to capture all of the heat either absorbed or released by a reaction

• Used to measure the exact amount of energy that enters or leaves during a chemical reaction

• Water is used to surround the reactions b/c it is stable nad has a high specific heat

The amount of heat absorbed or released during a physical or chemical change can be measured by the change in temperature of a … of water

The thermometer records water temperature. The water either absorbs energy from the sample, or transfers energy to the sample

known quantity

Change in temperature depends on (3):

1. Amount of heat energy added

2. Mass of the substance (how much substance) - a small amount of substance can be heated faster than a larger amount

3. Composition of the substance (what the substance is made of) - ex: metals heat faster than water

Specific heat

amount of energy required to raise the temperature of 1 gram of the substance by 1 Celsius

• depends on the physical properties of the substance - how good it is at absorbing energy

  • Heat quickly = low specific heat

  • Heat slowly = high specific heat

• Varies depending on the state of the material

water specific heat = ?

4.184 J/g°C

specific heat formula

q = mcΔT

enthalpy

heat of a substance at constant pressure

• no way to directly measure the enthalpy of a system, so we measure the change in enthalpy

Enthalpy change

• amount of heat that is absorbed or released by the system under conditions of constant pressure

• Equal to the difference between the enthalpies of the products and the reactants

  • (ΔH) = H_products - H_reactants

Heat of reaction

the amount of heat that is absorbed or released during a chemical reaction when the coefficients equals the number of moles

Thermochemistry equation

shows the amount of energy lost or gained during a reaction as part of the chemical equation

Most ionic compounds ionize in water (soluble in water). The water molecules pull the ionic compound into its …

component ions

The formation of an insoluble solid product (…) is the driving force of an aqueous reaction to occur

precipitate

The attraction between the ions of insoluble compounds is … than the attraction of the ions to water

stronger

spectator ions

Ions in an aqueous solution that sit around and watch the reaction

net ionic equations

shows only those particles involved in the reaction and is balanced in number of atoms and charge

When heat is absorbed by a substance, what happens to the kinetic energy of the particles in the substance?

The kinetic energy increases

When two chlorine atoms combine to form a molecule of chlorine, do the reactants or products have a higher potential energy content?

• reactants have more potential energy → forming bonds releases energy

  • Exothermic - reactants → products + energy

A sample of metal, at 120 degrees C, is placed into a calorimeter whose water is at a temperature of 10 degrees C. What will happen?

The water and metal will adjust to the same temperature between 10 degrees C and 120 degrees C.