Answer:
A. Endothermic reaction.
B. +150KJ.
C. 250KJ.
Explanation:
A. The graph represents endothermic reaction because the heat of the product is higher than the heat of the reactant.
B. Determination of the enthalpy change, ΔH for the reaction. This can be obtained as follow:
Heat of reactant (Hr) = 50KJ
Heat of product (Hp) = 200KJ
Enthalphy change (ΔH) =..?
Enthalphy change = Heat of product – Heat of reactant.
ΔH = Hp – Hr
ΔH = 200 – 50
ΔH = +150KJ
Therefore, the enthalphy change for the reaction is +150KJ
C. The activation energy for the reaction is the energy at the peak of the diagram.
From the diagram, the activation energy is 250KJ.
Answer: B. Concrete
Explanation:
Let N = reacting force pressing the bodies in context together (units in Newtons),
The question stated that the force pressing the two mounted/stacked objects together is equal to the weight of the object on top.
We need to start by finding the weight of the piece of wood.
friction is given by
f = μN
The value of f is 22.5,
and from the chart reference the coefficient of friction between wood and stone, μ is 0.30.
22.5 = 75. 0.30
Putting the values into the equation: 22.5 = 0.30N.
Divide both sides by 0.30 to find the value of N:
N= 22.5/0.3 = 75
Now that the piece of wood will be placed on another surface, its weight of 75 Newton is the force pressing the two bodies together.
To determine the new surface, you should find the new coefficient of friction by using the new value of the force of friction given 46.5:
46.5 = µ(75).
Divide both sides by 75 to isolate μ.
The refer chart also indicates that the coefficient of friction equals 0.62 between wood and concrete, so the new surface corresponding to 0.62 is the concrete, which is (B).