Exam II - Chemistry I

What does aqueous (aq) mean?

Dissolved in water

True or False: Given ideal conditions, it is possible for reactions to yield 100%

False

Why is the mole ratio used?

Because moles of reactants do not equation moles of products and because moles cannot be measured but grams can

What is equal on both sides of a reaction?

Atoms of reactants and atoms of products and mass of reactants and mass of products

What does the Law of Conservation of Matter state?

Matter cannot be created or destroyed

Why do we balance equations?

Chemical equations must be balanced to obey the law of conservation of matter

What are the 5 types of chemical reactions?

Combustion, Double Displacement, Single Displacement, Synthesis, Decomposition

What is a combustion reaction?

hydrocarbon burning in oxygen to produce CO2 and H2O

Precipitation reactions are what type of reaction?

Double displacement reaction

When compounds are dissociated what happens to the coefficient?

Coefficients are distributed to each term and the diatomic subscripts are turned into coefficients

What are redox reactions?

When there is a net movement of electrons within a reaction

What is oxidation?

Loss of electrons

What is reduction?

Gain of electrons

What is the oxidizing agent?

Substance that is reduced (causes oxidation)

What is the reducing agent?

Substance that is oxidized (causes reduction)

True or False: Fractions can be used to balance redox half reactions

True

True or False: Oxidation number rules are listed in order of importance

True

Sign before number

Oxidation

Sign after number

Charge

What are the 3 types of redox reactions?

Combination, Decomposition, and Single Displacement

How can decomposition redox reactions occur?

They can be thermal (occurring by heat) or electrolytic (occurring by the use of current

What is an acid/base neutralization reaction?

Double Displacement reaction without a precipitate

What is the Bronsted Lowry definition of an acid?

H+ proton donor

What is the Bronsted Lowry definition of a base?

H+ proton acceptor

What are the 7 strong acids?

HCl, HBr, HI, HNO3, H2SO4, HClO3, HClO4

What are strong bases made of?

Group1+Hydroxides(OH) and Group2+Hydroxides(OH) [except Mg and Be]

What do acid base reactions produce?

Salt and water

What are acid/base titrations used for?

Used to standardize or find the concentration of an unknown acid or base

What solution goes in the buret during acid/base titrations?

Acid/base with a known concentration

What solution goes in the beaker during acid/base titration?

Acid/base with unknown concentration with a specific amount

What is equal during the equivalence point of an acid/base titration?

mol H+=mol OH- (moles of acid=moles of base)

What is the difference between an endpoint and an equivalence point?

There is a slight (insignificant) excess of what is being titrated from the buret in the beaker at the endpoint, while at the equivalence point the chemical reaction comes to an end

How do we in a lab know that the reaction is complete during an acid/base titration?

An indicator (phenolphthalein) changes color indicating the endpoint is reached

What are the steps for calculating quantities for reactions?

1. Write chemical equation 2. Balance chemical equation 3. Calculate the moles given 4. Use the mole ratio from balanced equation 5. Convert moles to grams for what is needed

How do you determine the limiting reactant?

1. Convert reactants to moles 2. Divide by coefficient 3. Reactant with smaller number is limiting

What is the percent yield formula?

(actual/theoretical)*100

What is the percent error formula?

[(actual-expected)/expected]*100

How do you calculate how much excess reactant is reacted?

Multiply the limiting reactant by the molar ratio

How do you calculate how much excess reactant is left over?

Subtract excess given yield by calculated yield

What is thermodynamics?

The study of energy

What is thermochemistry?

The study of heat flow in physical/chemical change?

What are examples of physical changes in thermochemistry?

Transferring energy, changing states of matter, making solutions

What is an example of a chemical change in thermochemistry?

Chemical reactions

What is the difference between a system and its surroundings?

A system is a point of reference or the part of the universe being studied, while the surroundings are everything not in the system

What is the relationship between J and kJ?

1000 J=1kJ

What is the SI unit for energy?

J

What is the relationship between cal and J?

4.184J=1 cal

How much energy does it take to raise 1 degree of 1 gram of water?

1 calorie or 4.184 J

What do “+” and “minus” indicate in thermodynamics?

Direction of energy flow

Why is it vital to define a system in thermodynamics?

To determine which sign to use and the flow of energy

What is the difference between “minus” and “+” signs in thermodynamics?

“minus” means energy is flowing out of a system and energy is released, while “+” means energy is flowing into a system and energy is absorbed

What is a state function?

A property whose value does not depend on the path taken to reach that specific value

True or False: ∆Hreaction=0

False, ∆Reaction=∆Products

What is enthalpy?

A thermodynamic quantity equivalent of the total heat of a reaction or system

Why is the change in enthalpy discussed instead of just enthalpy?

It is easier to measure the change of enthalpy than just enthalpy

What is true in exothermic reactions?

H of reactants > H of products, ∆H < 0, usually hot because energy is released

What is true in endothermic reactions?

H of products > H of reactants, ∆H > 0, usually cold because energy is absorbed

What is on the Y axis of enthalpy diagrams?

Enthalpy, ∆H

How do graphs of enthalpy diagrams of endothermic and exothermic diagrams differ?

Reactants go on top and products go on the bottom for exothermic processes, while products go on top and reactants go on the bottom for endothermic reactions

True or False: The enthalpy (∆H) goes on the products side for endothermic reactions

False, ∆H goes the products side for exothermic reactions and goes on the reactants side for endothermic reactions

What is the specific heat capacity and its symbol?

c, heated needed to raise 1 gram of a substance by 1 kelvin or celsius

What is q?

Heat transfer

What is the q equation?

q=mc∆T

What determines the sign of q and makes it “+” or “minus”?

∆T, FinalT

When does q give off heat?

When q is negative

When does q absorb heat?

When q is positive

What are the 2 types of calorimeters?

Constant P (coffee cup) and Constant V (bomb calorimeter)

True or False: Temperature=energy

False, Temperature is measured in C/K, energy is measured in J/cal

What are calorimeters used for?

To determine the specific heat capacity of a metal sample

In calorimeters what is always equivalent?

Final temperature of water and final temperature of metal

What does ∆T mean?

Final temperature-inital temperature

What is the relationship between a system and its surroundings?

qin(absorbs heat)=-qout(gives off heat)

How do you calculate how much energy a reaction produces?

Multiple the molar ratio by the ∆H

Define Hess’s Law

Enthalpy of an overall reaction is the sum of the enthalpy of the step reactions that total the reaction, overall enthalpy=sum of step reactions

Why do we use/need Hess’s Law

Most reactions occur in multiple steps

Define Standard Enthalpy of Formation

Change in enthalpy when 1 mole of a substance at standard state is formed from is pure elements under the same conditions

What role does energy play in Standard Enthalpy of Formation

How much energy it takes/gives off when forming 1 mole of given substance

How does Standard Enthalpy of Reaction differ from Standard Enthalpy of Formation?

Standard heat of reaction (Standard enthalpy of reaction) is the sum of the standard heat (enthalpy) of reaction of the products minus the reactants

Why is the unit kJ/mol used for the standard of enthalpy of reaction problems?

Change in enthalpies have been calculated by standard enthalpies of formations, which is measured per mol

Why do moles cancel out when calculating standard enthalpy of reaction problems?

Moles of substance are been multiplied by standard enthalpy of formation, which is measured in kJ/mol

What is the standard enthalpy of formation of mono/diatomic elements?

0 kJ/mol