Module 07: Energy in Reactions Flashcards

Question

# 07.02 Enthalpy Values The substances below are listed by increasing specific heat capacity value. Starting at 30.0 °C, they each absorb 100 kJ of thermal energy. Which one do you expect to increase in temperature the least? (3 points) 1. Cadmium, 0.230 J/(g °C) 2. Sodium, 1.21 J/(g °C) 3. Water, 4.184 J/(g °C) 4. Hydrogen, 14.267 J/(g °C)

Answer 1

**4.** Hydrogen, 14.267 J/(g °C)

Answer 2

**1.** 65.2 kJ of heat are released for every mole of CaO that reacts

Answer 3

**3.** 29 °C

Answer 4

**4.** Sandy clay, because it needs to release less energy to decrease its temperature

Answer 5

**3.** 320 J

Answer 6

*System is the container or entity of interest* 1. Isolated System 2. Closed System 3. Open System

Answer 7

* neither energy or matter is premitted exchange with surroundings * total amount of energy = constant

Answer 8

* Energy can or leave, but matter cannot* * boundary between systems

Answer 9

*Both matter and energy are exchanged freely between the system and the surroundings*

Answer 10

*Change in a system that proceeds without a net input of energy from an outside source.* * not instantaneous * needs some activation energy to get started → without any continuing outside influence (heating, cooling, stirring) * fast/slow * Factor affects spntaneity: **change in entropy** (△S) - reaction or process takes place

Answer 11

In general, an _exothermic_ reaction will **increase the entropy** of its surroundings because it **releases energy**. An _endothermic_ reaction will **decrease the** entropy of the surroundings because it **absorbs energy**.

Answer 12

the property that describes the disorder of a system (S)

Answer 13

Rises from Solid → Gas Gas: **highest** Solid: **lowest** * Entropy increases as a substance changes to a less condensed state (solid to liquid or liquid to gas). This is because an increase in the motion of particles means an increase in disorder. Gas particles have many more positions and arrangements available to them than the same particles in the solid state. * Entropy increases when substances mix or something is dissolved because mixing particles together increases the disorder. * Entropy increases when the total number of moles of products is greater than the number of moles of reactants because a greater number of particles leads to a greater chance of disorder. * The entropy of any sample increases when temperature increases because of the increase in kinetic energy and movement. * Entropy is greater for particles with a greater mass. For example, one mole of Cl2 has a greater mass than one mole of F2, so the entropy of the chlorine sample is greater. * Entropy is greater for weakly bonded compounds than for strongly bonded compounds. For example, the carbon atoms in graphite have weaker bonds than the carbon atoms in diamonds, so the entropy is greater for the sample of graphite. * Entropy is greater for compounds with greater complexity (greater number of atoms, greater mass, etc.).

Answer 14

**the energy in a physical system that can be converted to do work**

Answer 15

***△G = △H − (T × △S)*** * △G: free energy change * △H: enthalpy change * T: temperature * △S: entropy change *At a constant temperature and pressure, a process is spontaneous in the direction that gives a _negative change in free energy_ (−△G).*

Answer 16

**2.** An open system, because heat and matter are both able to enter or leave the system

Answer 17

**2.** - ΔG

Answer 18

**3.** H2O_(l)→ H2O_(s)

Answer 19

**2.** Negative enthalpy change and positive entropy change

Answer 20

**1.** Any temperature, because combustion of ethane leads to an increase in entropy

Answer 21

**4.** An isolated system, because neither heat nor matter is entering or leaving the container

Answer 22

**4.** It has a positive enthalpy change and negative entropy change

Answer 23

**Calorimeter**: used measure heat absorbed or released by a chemical or physical change **Calorimetry**: measurement of change

Answer 24

* **determine energy gained or lost by the water in the calorimeter** * q → + (gain energy) & - (loss energy)

Answer 25

q_surroundings = −q_system m × c × △T = −(m × c × △T) \* negative sign: designate flow of every

Answer 26

**Step 01**: Indenfity known variables **Step 02:** Determine unknown variables **Step 03**: Calculate q_surroundings and q_system. **Step 04:** solve for c (specific heat)

Answer 27

q_surroundings = m × c × △T q_surroundings = 150.0 g × 4.184 × (18.3 °C − 15.0 °C) q_surroundings = 2,100 J q_surroundings = −q_system −2,100 J = 150.0 g × c × (18.3 °C − 75.0 °C) **c = 0.25**

Answer 28

***"For particles to react successfully, they must collide"*** * states rate of reaction is determined by the number of successful collisions * occur over a given amount of time _Successful Collision_: enough energy for reactants to intersect valence shells, create new bonds, make product Two Factors: 1. adequate speed of particles 2. correct orientation

Answer 29

More complex → more difficult align with one another * must collide energy equal/greater

Answer 30

*Represent distribution of particle energy within a sample at a given temperature* * activation energy requirement → **requirement for successful collisions** * under particles under this area: not enough energy to react * only particles represented on upper part: enough energy to react *When analyzing a Maxwell-Boltzmann distribution curve, a common mistake is thinking that the curve with the higher hump is the one with the greater temperature. Remember, the curve shows the number of particles with a given energy. But because temperature is a measurement of the average kinetic energy, the curve that has more particles with higher energy (or shifted right) is the one with the higher temperature. Therefore, in the graph above, curve T2 reflects a higher temperature than curve T1.*

Answer 31

1. Concentration and Rates 2. Temperature and Rates 3. Catalysts and Rates

Answer 32

* Increae concentation: **increase rate of a reaction** * Concentration higher: **chances of particles coming in contact increases** ## Footnote *Increase pressure or decreasing volume: _increase reaction rate_*

Answer 33

* slight increase temperature: changes distribution of energy in a sample * kinetic increase little amount → large increase number of particles meet and exceed activation eneryg * Reation not happen fast enough: raised temperature help

Answer 34

* temperature not increased meet activation energy needed * Catalyst: alternative path → less activation energy required * results larger percentage of successful collisions _Maxwell-Boltzman distribution_: lower activation energy requirements allows more partciles to meet energy requiremetns for successful collision without increase in temperature

Answer 35

*Rates: measures change in something over a given amount of time* Average rate of change: **change in concentration of a reaction over a time interval** * depends concentration of reactants present * decreases as reactants are used up * Concentration measured molarity (M)

Answer 36

**(Final Concentration - Initial Concentration)** **÷** **(Final Time - Initial Time)**

Answer 37

* **Dynamic** → reaction occurs in both directions * Dynamic equilibrium: rates of forwards and reserve reaction continues to occur* **A + B ⇄ C + D** * Forward reactions follow the right-pointing arrow in the equation and yield products. * Reverse or backward reactions follow the left-pointing arrow in the equation and yield reactants.

Answer 38

1. Rate of forward reaction = rate of reverse reaction 2. Concentrations of the reactants and products remain constant

Answer 39

* equal* * reaction not stop when in equilibrium

Answer 40

The evaporating and condensing phases of water continue back and forth in dynamic equilibrium.

Answer 41

Dynamic equilibrium is also possible during dissolving and crystallization, which are both physical changes. For instance, when salt dissolves in water, it doesn't change chemically; it just breaks apart. As more salt is dissolved in the water, it reaches a saturation point, and the salt begins to crystalize again. At this point, a balance has been reached in this physical process; salt is continuously dissolving at the same rate as it is crystallizing. The salt and water solution is in dynamic equilibrium.

Answer 42

* General description of the equilibrium conditions, including an equation defined the equilibrium constant* * **Equilibrium Constant**: (K) the value obtained when equilibrium concentrations are plugged into the law of mass action equilibrium expression; represented by the letter K, it is constant for a given system at a given temperature

Answer 43

* In the forward reaction, w moles of A react with x moles of B to produce y moles of C and z moles of D.

Answer 44

**a given set of equilibrium concentration values** * depends on intial concentration of each substance * predicted based on value of equilibrium constant

Answer 45

*Compares the reaction rates over time* * see when equilibrium happens * The point on the graph when the forward and reverse reactions reach **equal rates**, is when the reaction has reached dynamic equilibrium.

Answer 46

**describes the change in concentrations of reactants and products over time** * direct relationship between concentration and rates of reverse reaction * The point on the graph when both concentrations plateau and *remain constant* when the system has reached dynamic equilibrium.

Answer 47

**K \> 1** The forward reaction proceeds to the right, giving more products than reactants when the system reaches equilibrium. **K \< 1** The forward reaction will not proceed very far before equilibrium is established, and the system will have more reactants than products at equilibrium.

Answer 48

* equilibrium reactions want to stay in equilibrium → distrurbed through stress → **change concentration** to shift to a new equilibrium. * discovered by Henri Louis Le Châtelier Equilibrium reactions show the forward and reverse reactions occurring simultaneously using a double arrow pointed in both directions in the chemical equation. **A + B ⇄ C + D**

Answer 49

* A shift _right_ means the reaction moves in the **forward** direction and yields **more products.** * A shift _left_ means the reaction moves in **reverse** (backward) and yields **more reactants.**

Answer 50

* increases rate of reaction (providing alternative reaction path) * Lowers activation eneryg for both forwards and reverse reactions * **no effect equilibrium**

Answer 51

If a component (reactant or product) is **added** to a reaction system at equilibrium, the equilibrium position will shift away from what was added to _lower its concentration_. If a component is **removed** from a reaction system at equilibrium, the equilibrium system will shift to _replace some_ of what was removed.

Answer 52

When the pressure of an equilibrium system is **increased**, the system will shift in the direction that _decreases the total moles of gas_ in the system to minimize the stress. The opposite is true if pressure is **decreased**; the system will shift toward the side of the equation that has a _greater total number of moles of gas_.

Answer 53

When an equilibrium system is **heated**, the temperature increases in the system. It will shift forward (right) in an endothermic reaction and backward (left) in an exothermic reaction. When an equilibrium system is **cooled**, the temperature decreases. The system will shift backward (left) in an endothermic reaction and forward (right) in an exothermic reaction.

Answer 54

**4.** Shift it toward the side with lower total mole concentration

Answer 55

**1.** Adding more of gas C to the system

Answer 56

**4.** Increasing temperature

Answer 57

**3.** It will shift toward the reactant side as there are a greater number of moles of gas on the reactant side

Answer 58

**1.** This reaction is exothermic because the system shifted to the left on heating