Calculate the heat change associated
with cooling a 350.0 g aluminum bar
from 70.0/C to 25.0/C. Is the change
endothermic or exothermic? Why?
(-14.2 kJ)

Heat change is -14,175 joules, Exothermic

Explanation:

We are given;

We are required to determine the heat change and indicate whether endothermic or exothermic;

We know that;

Heat change = Mass of a substance × specific heat × change in temperature

In this case;

Mass of Aluminium = 350.0 g

Change in temperature = (25 - 70)

                                       = -45° C

Specific heat of aluminium = 0.90 J/g°C

Therefore;

Heat change = 350.0 g × 0.90 J/g°C × -45°C

                     =-14,175 joules

The heat change is exothermic because it is a negative value, also because cooling process involves heat loss and thus an exothermic reaction.

860 cm/s

Explanation:

Let P = momentum of wrench-man system before throwing the wrench and P' = momentum of wrench-man system before throwing the wrench.

From the law of conservation of momentum,

P = P'

P = 0 (since both Astronaut and wrench were initially stationary) and P' = m₁v₁ + m₂v₂ where m₁ = mass of wrench = 4g = 0.004 kg v₁ = velocity of wrench after releasing the wrench = -15 m/s m₂ = mass of Astronaut = 70 kg and v₂ =  velocity of Astronaut after releasing the wrench.

So, P = P'

0 = m₁v₁ + m₂v₂

-m₁v₁ = m₂v₂

dividing both sides by m₂, we have

v₂ = -m₁v₁/m₂

substituting in the values of the variables, we have

v₂ = -0.004 kg × (-15 m/s)/70 kg

= 0.06 kgm/s ÷ 70 kg

= 8.6 × 10⁻⁴ m/s

= 860 × 10⁻² m/s

= 860 cm/s