Chemical reactions!

Question 1

What is heat equal to in a closed system? What does it determine?

Answer 1

Enthalpy - determines that state of a substance (whether solid liquid or gas)

Question 2

What is the ideal gas equation? What is it used to find?

Answer 2

• pV=nRT
• It models the behaviour of gases under ideal conditions

Question 3

What is a reaction enthalpy?

Answer 3

ΔH(R) = H(products) - H(reactants)

Question 4

What is Hess’s Law?

Answer 4

The total enthalpy change of a reaction is the same no matter how many steps are taken to get there
- enthalpy change is independant of the route taken

One step or several - the energy change is equal

Question 5

What is enthalpy?

Answer 5

The total energy (heat) in a thermodynamic reaction

Question 6

What is entropy?

Answer 6

The measure of the disorder of a closed system - the larger the entropy, the mroe disordered the system

Question 7

What is the Gibbs free energy equation?

Answer 7

ΔG = ΔH - TΔS

Question 8

What must the ΔG value be for a spontaneous, exergonic reaction?

Answer 8

ΔG < 0

Question 9

What must the ΔG be for a non-spontaneous, endergonic reaction?

Answer 9

ΔG > 0

Question 10

What effect does a catalyst have on activation energy?

Answer 10

Lowers it - making the reaction more viable

Question 11

What is collision theory

Answer 11

How for molecules to react together they must have both a successful collison and enough energy (must be above the activation energy of the reaction)

Question 12

What is the Arrhenius equation?

Answer 12

k = A x e ^ -Ea/RT
- K = rate constant
- A = given in question
- e = Euler’s number
- Ea = activation energy
- R = Gas constant (given)
- T = Temperature in K

Question 13

How do you convert between degrees C and K?

Answer 13

+ 273

Question 14

What can be said about a reaction if k is negative?

Answer 14

Exergonic reaction - will not progress until Ea is provided

Question 15

What can be said about a reaction if k is positive?

Answer 15

Ea has been reached, and the exergonic reaction will occur

Question 16

What is the rate equation?

Answer 16

Rate = k [A]^x [B]^y
- K = rate constant
- x and y = orders of A and B

Question 17

What would happen to the rate if the concentration of a first order reactant were doubled?

Answer 17

The rate would also double

Question 18

What would happen to the rate if the concentration of a second order reactant were tripled?

Answer 18

The rate would increase 9x

Question 19

What would happen to the rate if the concentration of a zero order reactant were doubled?

Answer 19

Nothing - zero order reactants have no impact on rate

Question 20

What would a zero order reactant look like on a concentration time graph?

Answer 20

Straight negative line - the rate is independent of the reactant

Question 21

What would a first order reactant look like on a concentration time graph?

Answer 21

Exponential decrease, half life is constant over time

Question 22

What would a second order reactant look like on a concentration time graph?

Answer 22

Steeper exponential decrease, half-life increases over time as concentration decreases

Question 23

What would a zero order reactant look like on a concentration rate graph?

Answer 23

Straight horizontal line - the rate and concentration do not affect each other

Question 24

What would a first order reactant look like on a concentration rate graph?

Answer 24

Straight positive line through origin - the rate is proportional to the concentration

Question 25

What would a second order reactant look like on a **concentration rate** graph?

Answer 25

Exponential increase starting at the origin - the rate is proportional to the square of the concentration

Question 26

What are Van der Waals forces?

Answer 26

This is a general term for all intermolecular forces of attraction, including London forces, dipole-dipole forces, and hydrogen bonds.

Question 27

What are the weakest kind of intermolecular force?

Answer 27

London forces, found in alkanes

Question 28

What are London forces?

Answer 28

Temporary differences in distribution of binding electrons temporary partial positive and negative charges. Attraction depended on contact area

Question 29

What are dipole-dipole forces? Give an example

Answer 29

Based on permanently polarized bonds - occur between polar molecules and are stronger than London forces e.g. acetone

Question 29

What do hydrogen bonds require along with hydrogen? Give some examples of where they are found

Answer 29

Requires oxygen or nitrogen in organic molecules. Examples: DNA double helix, 𝛃 sheets and 𝛂 helices in proteins

Question 30

What is stoichiometry?

Answer 30

Stoichiometry is the area of chemistry that deals with quantitative relationships between reactants and products in a chemical reaction. It’s about how much of each substance is involved Basically maths - balanced equations etc.

Question 31

How do you calculate moles?

Answer 31

Moles = mass/molar mass

Question 32

How do you find the molar mass of a molecule?

Answer 32

Sum of all the atomic masses in the molecule

Question 33

How do you find concentration?

Answer 33

Concentration = moles/volume

Question 34

What does a phase diagram show?

Answer 34

Physical state of a substance under different temperatures and pressures

Question 35

What does the triple point of a phase diagram show?

Answer 35

The unique set of temperature and pressure at which all three phases (solid, liquid, and gas) coexist in equilibrium For water this is 0.01°C and 0.006 atm

Question 36

What does the critical point of a phase diagram show?

Answer 36

The highest temperature and pressure at which a liquid and gas can coexist

Question 37

What process takes you straight from a gas to a solid?

Answer 37

Deposition

Question 38

What process takes you straight from a solid to a gas?

Answer 38

Sublimation

Question 39

What is the 1st law of thermodynamics?

Answer 39

Energy cannot be created or destroyed — only transferred or transformed Matter has an energy content - enthalpy H

Question 40

What letter is enthalpy?

Answer 40

H

Question 41

What is the ideal gas law equation?

Answer 41

PV=nRT This equation relates Pressure (P), Volume (V), Amount of gas (n), Temperature (T), and the gas constant (R). Shows how pressure and volume directly affect gas equality

Question 42

What kind of reaction do you have if heat is the product using the ideal gas law?

Answer 42

Exothermic

Question 43

What kind of reaction do you have if heat is the reactant?

Answer 43

Endothermic

Question 44

How do you measure the change in enthalpy?

Answer 44

Hproducts - Hreactants

Question 45

What does Hess's law state?

Answer 45

The enthalpy of a reaction is equal to the sum of the enthalpies of the reactions into which it may be divided. The enthalpy of a reaction is independent of the route taken The total enthalpy change (ΔH) for a chemical reaction is the same, no matter how many steps the reaction is carried out in

Question 46

If Gibb's free energy is negative, is the reaction spontaneous?

Answer 46

Yes

Question 47

What is entropy?

Answer 47

Measure of disorder Larger the entropy, larger the disorder

Question 48

What is Gibb's free energy?

Answer 48

G = H –T.S

Question 49

What letter is used for entropy?

Answer 49

S

Question 50

What kind of reaction do you have if G is positive and non-spontaneous?

Answer 50

Endergonic

Question 51

What kind of reaction do you have if G is negative/less than 0?

Answer 51

Exergonic

Question 52

What is the activation energy?

Answer 52

Activation energy is the minimum amount of energy that reactant particles must have for a chemical reaction to occur

Question 53

What does catalysis do?

Answer 53

Lowers the activation energy and speeds up rate of forwards and backwards reaction equally

Question 54

What does the Arrhenius equation state?

Answer 54

The Arrhenius equation shows how the rate of a chemical reaction depends on temperature and activation energy

Question 55

What is the Arrhenius equation?

Answer 55

k = rate constant A = frequency factor (how often collisions occur in the correct orientation) Ea = activation energy (J/mol) R = gas constant = 8.314 J·mol⁻¹·K⁻¹ T = absolute temperature in Kelvin (K) e = Euler’s number (≈ 2.718)

Question 56

What kind of control are exergonic reactions under?

Answer 56

Thermodynamic

Question 57

What kind of control are endergonic reactions under?

Answer 57

Kinetic

Question 58

What does the 1st order rate law describe?

Answer 58

The 1st order rate law describes reactions where the rate depends linearly on the concentration of one reactant