Chemical Reactions

Question 1

Define enthalpy

Answer 1

The H Heat contained in a system

Question 2

Identify whether the enthalpy of a reaction would be positive or negative, based on:
Energy diagram
Temperature change

Answer 2

/\H > 0 = positve reaction and requires energy
/\H < 0 = negative reaction and relases energy

Question 2

Define /\H

Answer 2

Change in enthalpy during a chemical reaction
H products - Hreactants

Question 3

Draw an energy diagram from:
Exothermic reaction
Endothermic reaction

Answer 3

If it takes less energy to break apart bonds than released when forming new bonds then the reaction will release more energy than required - causing an increase of thermal energy in the surroundings causing an exothermic reaction, where the products are less than the reactants.

If it takes more energy to break apart bonds than released when forming new bonds then the reaction will require more energy than it releases. - causing a decrease in thermal energy in soundings as the reaction absorbs the heat, making it endothermic.

Question 4

Describe how energy changes during a chemical reaction; in terms of chemical bonds breaking and reforming

Answer 4

To break a bond energy is required
When a chemical bond is formed, energy is released

Question 5

Combustion

Answer 5

C H + O = CO2 + H2O

Question 6

Synthesis

Answer 6

A + B = AB

Question 7

Decomposition

Answer 7

AB = A + B

Question 8

Single Replacement

Answer 8

AB + C = AC + B

Question 9

Double Replacement

Answer 9

AB + CD = AD +CB

Question 10

Acid-Base Neutralization

Answer 10

Acid + Base = H + OH + salt

Question 11

Law of conservation of Mass:

Answer 11

Total mass in a closed system does not change during a chemical reaction

Question 12

Closed system

Answer 12

Nothing can enter or leave

Question 13

Open system

Answer 13

Things can enter and leave

Question 14

Acid

Answer 14

below 7

Question 15

Base

Answer 15

above 7

Question 16

Equivalence point

Answer 16

when acid and base reaction becomes neutral

Question 17

standardization

Answer 17

determining the concentration of a solution by titration

Question 17

endpoint

Answer 17

when the indicator changes color

Question 18

Indicator

Answer 18

a chemical whose color changes at different pH levels.

Question 18

pH

Answer 18

scale used to determine the acidity and basicity of a solution

Question 19

What is neutral?

Answer 19

water and salts, NaCl, H2O

Question 20

Define titration and identify the purpose of the procedure:

Answer 20

a chemical analysis method to quantitatively determine the concentration of a solution
- the unknown concentration solution is reacted with a solution of known concentration
- color change is used to determine the endpoint of the reaction

Question 21

Why perform a titration?

Answer 21

to verify the concentration of a solution that has been created

Question 22

Give the steps to perform a titration and identify techniques used to minimize error (lab skill)

Answer 22

Rinse the burette with the NaOH(aq) solution and fill it with fresh NaOH(aq) solution. (use a funnel) then put the burette into the clamp on the support stand.
Record the initial volume of titrant in the burette to the nearest 0.05 mL.
With a clean, dry 10.00 mL volumetric pipette and bulb, draw up a 10.00 mL sample of the HCl solution.
Transfer the 10.00 mL HCl sample to a clean 125 mL Erlenmeyer flask and add two drops of phenolphthalein indicator, then swirl
Position the flask under the burette. With a sheet of white paper/tile under the flask (to better observe color change), slowly titrate(add) the NaOH(aq) standard solution into the HCl sample. Gently swirl the flask as you add the titrant to mix the solutions.
** As the endpoint is approached, you will see a slight color change that will disappear with swirling. Now add the titrant to the flask, drop by drop. You have reached the endpoint when the indicator permanently becomes light pink, after swirling. **
Record the final volume of the titrant in the burette and the indicator color.
Repeat Steps 3–9 three more times or until you have several results in which the volumes of titrant added are the same to within ± 0.2 mL. Remember to record the initial volume of the titrant before each trial, and refill it with NaOH(aq) as needed.

Important things:
Rinse the burette and pipette with a solution first
Don’t overshoot the solution

Question 22

Describe what a limiting reactant and excess reactant are, in terms of the amount of product(s) formed

Answer 22

The limiting reagent in a chemical reaction is the reactant that will be consumed completely. Once there is no more of that reactant, the reaction cannot proceed. Therefore it limits the reaction from continuing. The excess reagent is the reactant that could keep reacting if the other had not been consumed.

Question 23

What does mole ratio mean?

Answer 23

The ratio between the relative number of moles of any two substances in a chemical reaction. Based on the coefficients of the substances in a balanced chemical equation, the coefficients can also be used to represent the number of molecules used/produced in a chemical reaction.