Heleleppe
the purpose of this exercise is to make a hypothesis about the effect of changing an independent variable.
1. what effect you would expect different diameter gears to have on the speed of the car?
2. select your hypothesis from the choices below and copy your choice here: i think with larger gears the car moves
(a) faster
(b) slower
(c) the same speed
procedures for exercise c: make observations
the purpose of this exercise is to record data on the performance of the cart based on its configuration.
1. the student began trials of the car with the different gears, starting with the smallest gear (3.5cm). she wound up the spring and lifted the lever to release the cart.
2. she clicked stop on the timer as the cart crossed the finish line. the timer shows the amount of time needed for the cart to travel 1 meter.

answer:

break it down

explanation:

when 25.0 ml of 0.700 mol/l naoh was mixed in a calorimeter with 25.0 ml of 0.700 mol/l hcl, both initially at 20.0 °c, the temperature increased to 22.1 °c. the heat capacity of the calorimeter is 279 j/°c.

the equation for the reaction is:

naoh + hcl → nacl + h₂o

moles of hcl = 0.0250 l hcl ×

0.700

mol hcl

1 l hcl = 0.0175 mol hcl

volume of solution = (25.0 + 25.0) ml = 50.0 ml

mass of solution = 50.0 ml soln ×

1.00

ml soln

= 50.0 g soln

δt=t2-t1

= (22.1 – 20.0) °c = 2.1 °c

the heats involved are

heat from neutralization + heat to warm solution + heat to warm calorimeter = 0

q1+q2+q3=0

nδh+mcδt+cδt=0

0.0175 mol ×

δh

+ 50.0 g × 4.184 j·g⁻¹°c⁻¹ × 2.1 °c + 279 j°c⁻¹ × 2.1 °c = 0

0.0175 mol ×

δh

+ 439.32 j + 585.9 j = 0

0.0175 mol ×

δh

= -1025.22 j

δh=1025.22j0.0175 mol= -58 600 j/mol = -58.6 kj/mol

the answer is b. dilution