CHME 361 Exam 4 Pt 1

If the temperature is increased, what happens to the rate of a reaction?

The rate increases

Compute the standard voltage for the reaction Fe(s) + 2H+(aq) →Fe2+(aq) + H2(g).

0.44

Which half-reaction has the greatest tendency to proceed to the right as written?

E

How does the rate of corrosion depend on the voltage driving force?

No general correlation exists between voltage and corrosion rate.

In general, how does the rate of wet corrosion compare with the rate of dry oxidation?

Wet corrosion is faster

How do the diffusion rate of metals ions in water compare with the diffusion rates of the same ions in a solid oxide film?

Diffusion in water is much faster

Which half-reaction has the greatest tendency to proceed to the left (i.e., backwards)?

A

What does aerated water contain?

Dissolved oxygen

Which word denotes a surface at which a chemical species loses electrons?

Anode

Which word denotes the loss of one or more electrons

from a chemical species?

Oxidation

The figure above represents one way to protect a steel pipe from corrosion. Which reaction occurs at the cathode?

O2 + 2H2O + 4e— → 4OH—

The figure above represents one way to protect a steel pipe from corrosion. Identify the cathode in the figure.

Steel pipe

The figure above shows one way to protect a buried steel pipeline from corrosion. Which way do the electrons travel?

Right to left through the wire

Which term refers to the formation of a stable protective film in a particular environment?

Passivation

The figure above shows one way to protect a buried steel pipeline from corrosion. Identify the anode in the figure.

Scrap iron

The figure above represents one way to protect a steel pipe from corrosion. Which reaction occurs at the anode?

Mg → Mg2+ + 2e—

What causes weld decay in stainless steels?

Depletion of chromium in the HAZ

Which term indicates that a metal has no tendency to oxidize at all in a particular environment?

Immunity

The figure above shows one way to protect a buried steel pipeline from corrosion. Identify the cathode in the figure.

Steel pipe

What is the term for steel coated with a sacrificial layer

of zinc?

Galvanized Steel

Why is titanium (Ti) less effective as a sacrificial anode than magnesium (Mg) or zinc (Zn)?

Ti tends to passivate

The figure above represents one way to protect a steel pipe from corrosion. Identify the anode in the figure.

Magnesium Slab

Suppose the box is sliding at a constant speed of 0.6 m/s. If μs= 0.6 and μk= 0.4, what is FT (in newtons)?

4

Which process removes material from surfaces by shearing off asperity junctions that are bonded together?

Adhesive Wear

Suppose the box starts at rest. If the force on the string is increased until FT = 2 N, what is the magnitude (in newtons) of the frictional force acting on the box? Assume μs = 0.6, and μk = 0.4

2

If FT = 0 N, μs = 0.6, and μk = 0.4 what is the magnitude (in newtons) of the frictional force acting on the box when it is stationary?

0

If μs = 0.6 and μk = 0.4, what is the magnitude of the normal force F⊥acting on the box (in newtons)?

10

When two services remain together without moving, local atom-to-atom bonding can occur at junctions. What effect if any does this have on the relative magnitudes of kinetic and static friction?

Bonding makes static friction greater than kinetic friction

Which process reduces friction by contaminating asperity junctions with active molecules?

Boundary lubrication

In which process do hard particles remove material from a surface?

Abrasive wear

Suppose the box starts at rest. If μs= 0.6 and μk= 0.4, what is FT (in newtons) when the box is just about to start sliding?

6

What is the term for a projection on a rough surface?

Asperity

Which property of a bearing material allows it to remove dirt particles from circulation?

Embeddability

Which property of the bearing material allows it to adjust to minor misalignments?

Conformability

What determines the maximum pressure at which a bearing material may operate?

Yielding

Where is high-hysteresis (high-loss) rubber used in tires, and why?

In the tread, to improve skid resistance

Which process involves the reduction of friction between two surfaces by adsorbed active molecules?

Boundary lubrication

What determines the maximum velocity at which a bearing material can operate?

Heating

Which property explains why the work of compression is not completely recovered when the rubber relaxes to its original length?

Anelasticity

Where is rubber used in tires, and why?

In the tire wall, to frictional losses

Which process reduces friction by a full viscous film between two surfaces?

Hydrodynamic lubrication

What is case-hardening?

Hardening of the exterior of a steel component

Why is borosilicate glass such as Pyrex preferred over ordinary soda glass for making laboratory glassware?

Borosilicate glass has a lower expansion coefficient

Consider the following equation: σ=−αEΔT. Why is the negative sign included in this equation?

Heating a constrained solid creates compressive stress.

Sometimes the lids on screw-top containers can be difficult to remove by hand. Under what conditions can putting the closed container in hot water assist in removing the lid?

The lid material has a higher a than the container material.

A solid is placed in a refrigerator, where it experiences a

temperature change ΔT=−20∘C. What is this temperature change

in kelvins?

-20

How are bridges designed to allow for thermal expansion?

(Check all that apply.)

Roller bearings are used to support

spans; Spans are separated by expansion joints.

A pure copper rod, initially 10 cm long, is heated from 273

K to 338 K. Calculate the stress in the rod if its ends are constrained during heating. Be sure to include the proper sign, and express your answer in MPa. You may assume the following material properties for copper: Elastic modulus: 115 GPa; Poisson ratio: 0.33; Yield strength: 69 MPa; Tensile strength: 220 MPa; Thermal expansion coefficient: 17.0 ×10^(–6) K^(–1)

-126

What is broadly true of the relationship between the elastic modulus and the thermal expansion coefficient for most materials?

The greater the modulus, the lower the thermal expansion coefficient.

A pure copper rod , initially 10 cm long, is heated from 273 K to 338 K. Calculate the change in the length of the rod if its ends are free to move. Express your answer in millimeters (mm).

0.11

A solid is placed in a refrigerator, where it experiences a temperature change ΔT=−20∘C. What is this temperature change in Fahrenheit?

-36

Traditional railroad tracks consist of relatively short lengths of steel connected by bolted joints. Newer railroad tracks consist of continuous welded rails. What measures are taken to prevent damage by thermal expansion or contraction of the continuous rails? (Choose all that apply.)

[All but hydraulic jack compression]